# Defensive Ferments of the Animal Organism/Defensive Ferments of the Animal Organism/Section 1

Defensive Ferments of the Animal Organism.
The question has frequently been raised, whether unicellular organisms exhibit simpler processes, in their general organization and metabolism, than do organisms composed of numerous cells. A priori, it is conceivable that organisms of a morphologically simpler construction are composed of simpler combinations, and that their metabolic processes follow a simpler path, than is the case in those forms of life in which the body is built up by the co-operation of different cells. But all our experience, hitherto, has proved, that even those cells which are constructed on a simple plan morphologically do, when studied from a purely chemical point of view, show exceedingly complicated relations. Indeed, the study of the processes of metabolism in unicellular forms of life is a study all the more difficult, in comparison with that of more complicated organisms, in that, in the former, it is so difficult to separate the actually ​absorbed materials from the metabolic by-products, and these again from the secretory or excretory products. Absorption and secretion merge in each other. The higher we climb in the scale of organization, particularly in the animal kingdom, the more do we meet with cells which are entrusted with special functions. For instance, we find cells which receive matter from the exterior. Others transform particular compounds into products of a special nature. Others, again, have the function of carrying the final products of metabolism to definite points for excretion.
A unicellular organism stands constantly in relation with numerous substances of the outer world, which differ from place to place and from time to time.. Some of these it makes use of as nutriment. Others, on the contrary, are entirely useless to the cell in question, while many would cause considerable harm, if allowed to penetrate its wall cells. To these substances the single cell does not yield itself helplessly, but has at its disposal various arrangements for its own defence. It has, in the first place, a cell wall which is impermeable by many substances. Further, the cell, by means of different processes, is capable of altering substances, which may in any way be injurious to it, in such a way that the active group is rendered harmless. Often a simple hydrolytic decomposition is sufficient to deprive the ​complicated substance of its specific properties. The disharmonious product is decomposed into indifferent by-products which are harmless to the cell. More energetic means are often employed, and the material is oxidized or reduced according to the special needs of the cell. Even in these simple forms of life it is probable that many substances are rendered harmless by combining to form fresh compounds, just as, in the metabolism of a more complicated organism, rearrangements of different kinds are undergone which alter such materials as are undesirable, so that they may be excreted in this form out of the body. Very often a given substance is incapable of combination, in which case it must first be so transformed by special processes as to be susceptible to combination. We thus see how the cells of the body oxidize, reduce, or decompose, until a product is reached that is capable of combination. There is no reason to doubt that unicellular organisms have similar means of defence at their disposal, but they are not so easily traced, owing to the fact that it is more difficult to add certain substances to a single cell, without damaging it, than it is in the case of a more complicated organism. The latter are able to modify profoundly the action of substances introduced by the mouth, owing to the fact that they are gradually absorbed. Further, these substances are considerably diluted in the lymph ​and the blood. Finally, they may be easily withdrawn from the body before they have had any opportunity of penetrating into the interior of the cells.
As a principal defence a single cell always has the cell wall, with its characteristic construction and its specific physical properties. Besides this, there is no doubt that ferments play a considerable role. They allow the cell to make a choice from amongst the substances which are continually acting upon it. These ferments, as Emil Fischer (Lit. 6) has proved from his exact researches on the subject, are directed in a specific manner against definite substrates. Only those substances, which are capable of being decomposed by the cell into simpler groups, are in general found to be of use to it. Throughout, our positive knowledge has led us to the conclusion that cells supply their vital needs only from the simplest units of the nutritive material, and that they probably never break down such complicated substances as fats, polysaccharides, and proteins, directly into their final metabolic products. Even the simplest units are not at once completely broken up. The cell works in stages. First of all it splits up large molecules into smaller particles, and so sets free from the rest one fraction of the entire ​energic contents of the original material, until finally—at least, with carbohydrates and fats—the whole amount of contained energy is released. The cell regulates its own metabolism down to the minutest details. In the proper preparation of the material to be decomposed, and in the gradual liberation of the amount of energy required, lies the real importance of those substances formed by the cell, which we at present comprise under the name of ferments.
The ferments have yet another value for the cell, in that they help it to regulate its own structure. Not every product which is taken up by the cell passes into its structure. Sometimes the decomposition must be carried on further; in other cases the particles must be synthesized suitably for the production of the necessary structural unit; after which it sets about the recombination of all the numerous constructive units, so as to form the complicated characteristic structure of the cell. Though we do not yet know the precise nature of the ferments, yet their specific activities, and their great importance in regard to cell metabolism and cell structure, are well known.
Without energy no cell can do work or produce heat, and it is in energic metabolism that we find a true picture of the functions of the cell. How the cell procures the required energy, in what manner it makes use of it, and so on, we can learn only by ​an accurate and possibly exhaustive study of the finer metabolic processes that go on in the cell. In these processes the so-called ferments play the most important rôle. With their aid we have succeeded in following up, outside the cell, processes which seemed to be exclusive properties of the cell. The more these experiments are extended, the more we meet with observations which show that we have been in the habit of picturing far too schematically the processes within the cell body. Thus, for instance, the simply formulated process of the fermentation of grape sugar into alcohol and carbonic acid gas—C$_6$H$_{12}$O$_6$ = 2C$_2$H$_5$OH + 2CO$_2$—has been found to be a most complicated process. A whole chain of reactions takes place, before the grape sugar is finally converted into alcohol and carbonic acid gas. There are many more intermediate stages present than were ever suspected. It will be an important duty of future research to ascertain what importance alcoholic fermentation, in all its stages, has for the yeast cell. We are indebted to recent researches, in which Knoop, Neubauer, Friedmann, Embden, Dakin, Schittenhelm, Jones and others have taken a prominent part, for a knowledge of numerous intermediate stages in the decomposition of the amino-acids, of grape sugar, of purin bases, &c. Every time we demonstrate fresh intermediate links in the decomposition of certain compounds we get a ​deeper insight into the working of the metabolic processes of the cells, and obtain important clues as to the means by which the cells of the animal organism produce, from compounds of a definite kind, substances that belong to a different group. We may mention here, for instance, the conversion of amino-acids into grape sugar, and of carbohydrates into fats.
Some of the unicellular forms of life, and some organisms consisting of a few groups of cells, are, at least in part, equipped with agents (ferments) which are not so precisely directed against certain substrates as the ferments of the higher species, such as plants and animals. While the ferments of the latter, so far as we know, principally decompose substrates consisting of units which are found in the cell-constituents that constantly recur in Nature, cases have been observed amongst the lower organisms (i.e., morphologically lower) where the latter split up compounds, which have been prepared in the laboratory from units which are not known to exist in a free state in Nature. Owing to this wider independence these organisms are assured of better conditions of existence. These cells can live where others, being unable to secure the energic contents of the material supplied to them, and being also unable to form from this substrate the elements required for their bodies, are bound to perish through lack of nourishment. In ​this way a cell dies, though it be plentifully surrounded by a material rich in energy, which, however, cannot be used because it lacks the proper form—both structural and configurative. It does not suit the organization of the cell. There is an abundance of oxygen at its disposal, but the latter cannot find any point of attack; and so the necessary preparation is wanting.
Some of the substances cannot be absorbed by the cell, simply because they are physically too coarse to penetrate through the cell wall. Such is the case with many colloidal substances, which must be first decomposed into simpler groups before they can pass into the interior of the cell. In these cases the presence of ferments is essential, and they have to be of such a kind as to be capable of decomposing the complicated molecules into a form which may easily penetrate through the cell wall. Often, however, such conditions may suffice as enable the coarse complex substance to be simply broken up into finer particles, which may be ingested in this form by the cell, without any molecular decomposition being necessary. Further decomposition takes place during absorption or, even later, at a suitable point within the cell.
Even a unicellular organism does not enter into intimate relations with substances which have not previously been remodelled. This remodelling ​generally takes place in such a manner that the substrate is decomposed into simpler indifferent constituents, after which the cell builds from the base upwards. In many cases this rebuilding is unnecessary. Such is the case when the cell only requires the energy contained in the absorbed substance. As soon, however, as substances are required as vital units of the cell, then they have to be adapted to the whole structural plan in all its minutest details. This is also the case when secretory substances, having a characteristic structure and a specific action, are to be formed.
Ye know of unicellular organisms which produce their body substance from very simple elements indeed. Thus, we know of organisms which produce their cell plasma from carbonates, nitrates, water, and salts. Others can draw their nitrogenous supply from any substance which will supply them with ammonia. Others, again, make use of the free nitrogen of the air. There are, however, even amongst unicellular organisms, some that are very fastidious and will only thrive in the presence of certain peptones. Others even require certain forms of protein from which to obtain their derivatives.
An exhaustive study of the sources of nitrogen ​necessary for each separate organism, paying due attention to other nutritious materials and conditions, will no doubt lead to exact methods for the culture of separate cells in the laboratory. Following this line of inquiry we could surround certain microorganisms with peptones whose composition we are familiar with, and so acquire a deeper insight into the processes of their metabolism. Even the mode of decomposition of the substrate, and of the intermediate stages, may furnish some important hints as to the specific functions of the cell and, in many cases, allow us to recognize particular organisms. We shall, by this means, understand why certain germs thrive upon certain media, while on any other substrate they either cease to grow or perish entirely.
It will also be possible to determine exactly, which of the decomposites and by-products formed from the culture medium produce harmful effects.
There is no doubt that, in the organic world, certain species prepare the soil for others, and in this way one organism acts as a pioneer to the others. It is a most interesting task to follow up this co-operation of different living beings in all its details. To a certain degree we have, in the co-operation of single ​cells, a forecast of the division of labour found amongst the organs of the higher forms of life. In the former case we have the cells as yet free, while in the latter they are combined into tissues. From this point of view we may look upon the symbiosis of heterogeneous species of cells as a first experiment in the building up of a cell state. The single cells are still independent and their duties multifarious. There is no strong bond uniting the organisms into any one "organ," and yet they depend upon each other for mutual support. Unicellular beings begin to organize themselves into combinations. Another step further and we arrive at cell complexes having definite functions, which we call organs. But even the most developed organisms, both of the animal and plant worlds, have relations with cells which stand outside the common organization. By means of micro-organisms the plant gains access to otherwise inaccessible sources of nitrogen, while by means of bacteria the animals make use of the important carbohydrate, cellulose. The bacteria convert the latter, within the intestines, into products which can be further decomposed by the ferments secreted by the glands.
In those organisms in which division of labour has been instituted amongst the cells, and particularly in those in which definite cells have closed in to form an alimentary canal, these are the only cells which ​are in communication with the outer world. They alone know, so to speak, what food is ingested. Even these have no direct relation with the ingested material, seeing that the latter, before being taken up by the cells of the gut, has been subjected to the action of the ferments poured into the alimentary canal, and been disintegrated into simpler and indifferent particles. All nutriment of a composite nature is dissolved in stages, until finally products of decomposition result which no longer exhibit any special characters.
Generally speaking, food supplies the material for the building up of the cell, and we must remember that we are dealing with the complicated tissues of animals and plants. Each cell has a specific fabric of its own, which is dependent on the nature of its separate units, and on the manner in which they combine together. We must not look upon this from a purely chemical point of view alone, but should pay attention to its physical aspects as well. The sum of the properties resulting from the special structure of the cell conditions its special functions. When such cells, with their specific structure and functions, are taken in by an individual organism, the latter can at first do nothing with the material supplied. The special character of the different products that make up the particular cells must first be destroyed. Unit must be separated from unit, so as to leave only a mixture of simple ​compounds, from the elements of which the body cells may construct their own material, or else renew their supply of energy. In the latter case, too, as has been mentioned before, a preparatory decom- position (a kind of adaptation to the cell) is necessary.
An analogy may be used to make clear this kind of reconstruction. Suppose an architect is called upon to convert a certain building, which has been specially designed for a particular purpose, into one suitable for an entirely different object. He would only be able to carry out this work on the condition that he might pull down the original structure. He would naturally be able to work some of the bricks of the old building into the plans of his new one. Some of the bricks, or even combinations of bricks, may be used as they are, others will have to be recut, while others, again, are of no value whatever. In just the same way does the animal organism act towards the specifically constructed parts of the cells which are used as food. First of all comes the disintegration into simple compounds, and then a reconstruction, according to entirely new plans, on the other side of the intestines.
The simplest conditions, in this respect, are to be seen amongst mammals during the suckling period, when, under normal conditions, the animal imbibes the milk peculiar to its species. This, as G. von Bunge first demonstrated very precisely, is in every ​respect adapted to the growing organism (Lit. 2, 3). The great point is, that the suckling is constantly supplied with the same mixture of salts and the same organic nourishment, namely, albumen, carbohydrates, and fats. Later, when mixed nourishment is taken, the conditions become much more complicated, according as greater quantities of this or that unit are introduced during digestion. The cells of the intestines are continually confronted with new duties, and have to adapt themselves gradually to the new conditions.
The cells of the milk glands are charged with the proper choice of food. They prepare the food for the developing organism, and simplify in particular the task of the intestines which, with the help of the liver, prepare the ingested food for the other cells of the body. Even the components of the milk, before they can be of any use to the organism, must be first considerably altered in the intestine, just as later, in the case of mixed food, a complete decomposition by means of the ferments precedes absorption. The difference in respect to the latter mode of nourishment only lies in the fact that, with the milk food, the same stages of decomposition, giving rise to the same by-products, always recur. Day after day, to a certain extent, the cells of the intestines and of the organism have to perform the same task.
From this point of view we may discern three ​important stages in the nutrition of the young of the mammal. Right up to its birth, which is the first stage, the fœtus has received from the mother only food which is in harmony with her body, and it makes this harmonize with its own blood and its own cells. Its organism has never come into contact with entirely disharmonious substances, and thus its metabolic processes run on definitely balanced lines. But birth supervenes, and with it the first change in the mode of nourishment. The individual has become independent. Respiration begins, and the cells of the lungs immediately enter upon their duty of exchanging gases. With equal rapidity the cells and glands of the intestinal walls undertake their new functions, which are, with the help of ferments, to prepare new nourishment for the cells of the body. The mother facilitates this task by giving off a supply of milk that is adapted to the requirements of the infant. In the first place, the intestinal cells have their task simplified. They never come into contact with a continually changing mixture of ions, nor are they overwhelmed with all kinds of disintegrated organic by-products. In this way the as yet inexperienced being is gradually accustomed to its new functions, and finds itself at last well prepared when it has to deal with a new kind of food which requires it to exercise its functions in a more variable, and, consequently more difficult manner. From the moment of parting ​with the milk as sole nourishment, from the moment of passing on to the mixed nourishment that is peculiar to its species, the second important change in the feeding of the growing individual is accomplished. The third stage of its evolution has begun.
The cells must function quickly to prevent disharmonious substances from entering the circulation. To ensure the proper discharge of a duty so important to the organism, the liver is placed between the intestines and other organs. Within this important organ the blood, still laden with the absorbed and partly metamorphosed food-stuffs, comes into contact with the liver cells. This material is once more thoroughly sifted, and the blood is finally discharged into the general circulation, freed from all substances that would be out of harmony with the body and the blood.
The knowledge that digestion is the means by which unsuitable products are prevented from passing into the blood and the cells of the body is of the greatest importance for our comprehension of the whole metabolism of the animal organism. Thus, to a certain extent, we may look upon the animal organism as a whole in itself. All the cells of the ​body have a common architecture, which is bequeathed from generation to generation by means of the sexual cells. The cells which combine into an organ have, besides that, a structure specific for the organ. We are bound to accept this view, otherwise it would be incomprehensible why, for instance, the cells of the liver should produce only bile, and the cells of the medulla of the suprarenal bodies adrenalin, &c. All the cells of the body have certain functions to perform which are of use to the whole organism. It is quite certain that the different organs supply substances to the blood, which set up definite processes in other particular parts of the organism. If these substances are to act effectively, they must have a definite specific structure. The cells, too, on which they are destined to act, must also be characterized by a special structure, otherwise it would be difficult to understand why a special secretion acts only upon certain cells, and leaves a number of other cells quite unaffected.
A particularly fine example of the specific action of gland secretions upon cells of specific structure is supplied by such cases of hermaphroditismus verus as that, for instance, in which the bullfinch is found to have a testicle on one side and an ovary on the other. These peculiar animals have on the one side male, and on the other female, plumage, each being delimited accurately, and without any transition, along the middle line of the body. It is absolutely ​impossible to imagine that the gland secretions of the two different glands, which bring about the full development of secondary sexual characters which are obviously present from the first, should remain only on one side of the body. They must, in fact, be carried by the blood to all the cells of the body. Nevertheless, the secretions of the male gland pass only to those cells which have "male" properties, and vice versa, the secretions of the ovary affect only the cells of the "female" half of the body.
Strong support for this view of a specific cell structure is supplied by the numerous experiments on transplantation. The surgeon nowadays tries, as much as possible, to retain the full strength of the functions of every organ, and, if some of the tissues are missing, he seeks aid in substitutes. It is found that only those tissues graft which are taken from the same species, while still better results are obtained by the use of parts of the same individual. Heteroplasty, i.e., the attempt to graft foreign tissues, has never succeeded. A body requires cells in harmony with itself. If they are in close relation, as is the case in tissues of the same species—even the individual has its own type—then it is very probable that with time the newly grafted tissue will, by means of reconstruction, assimilate itself with the other cells of the same organ, and so eventually with the entire organism.
​Finally, pathology provides us with a large number of cases supporting our view of the specific structure of the different cells belonging to a given organism. We know that certain poisons have an injurious effect only upon very definite kinds of cells. We might here refer to the well-known system diseases of the central nervous system. The so-called metasyphilitic phenomena, for instance, manifest themselves, only in very special regions of the spinal cord and the brain.
The idea that each kind of cell has its own structure, and to some extent its own metabolism, opens up a wide vista for therapy also. So far as the organism always forms products which act upon certain cells and only upon these, it must be possible to find substances which will act only upon those cells whose metabolism we may wish to alter in some way or other, or whose complete destruction is desirable. The latter is the aim of the battle waged against germs of infectious diseases and tumour cells, especially cancer. There is a great future for cell-specific therapy, which will pay special attention to the structure and the configuration of the means employed, or else attempt generally so to modify the chemical and physical conditions in certain cells that life will be impossible for them.
The admission of a certain specific structure, for each cell species with special functions, implies that each separate cell possesses special means enabling it ​to regulate its own structure. The components of the blood plasma, which serve as the deriving material, are the same for all cells. The formation of a specifically acting secretion also requires that every kind of cell should have means and arrangements at its disposal for the specific transformation, under certain circumstances, of the same product. From this point of view we should expect to find that each kind of cell controls particular ferments, of which, however, some will be common to all the cells of the body. These ferments have the task of decomposing the nourishment, brought by the blood plasma to the cell, into simpler products. Investigations on the peculiarities of cell ferments—the tools of the cells—are already in progress, and we shall deal with this question later on. It may be that the result of these investigations will supply the most unequivocal and sure support for the theory of the dependence of cellular function on cellular structure.
For the maintenance of a regular and undisturbed flow in the varied processes of the cell, we must assume that within certain limits constant conditions prevail. When we carry out certain experiments in a laboratory and try to study, for instance, the interaction of two substances upon each other, we choose the most favourable conditions possible, and take particular precautions against the presence of any ​other substances than those essential to the reaction. It is a well-known fact that the slightest contamination may influence the reaction to a very great extent. It may either fail altogether, or be retarded, or may even be diverted into quite a different direction. We meet with great difficulties if we have to follow up several reactions in one and the same medium. Intermediate products mav act, one upon the other, to such an extent that we arrive at a series of final products whose origin it would be extremely difficult to account for. Now, if in an animal organism the separate processes were not regulated in a very strict manner, and if, for instance, the blood did not receive substances which are in harmony with it, that is, always transformed in a definite and regular manner, it would be difficult for us to understand how the separate secretions always attain their aims in a very certain way, and how they are able locally to attack particular metabolisms, and either retard, or hasten, or initiate them.
There is not the slightest doubt that the course of this metabolism, as well as the inter-relations of the cells of a particular organ, is only imaginable under the supposition that the metabolism of the whole organism is regulated in the most precise way, not only quantitatively, but also qualitatively. We are bound to imagine that, in the work of the cells, the same stages of decomposition recur regularly, and ​that it is at a quite definite stage that the by-products of metabolism are passed by the cells into the lymph channels, and so into the blood system. The individual cell is in this sense responsible for the constant composition of the contents of the blood, in the same way as the cells of the bowels with their respective ferments.
Here, again, the animal organism controls important weapons of defence which may correct any possible errors. Between the blood and the cells of the body lies the lymph. The latter is the first to receive the substances supplied by the individual cells, and controls them by means of its accessory apparatus, namely, the lymph cells and the glands. Some of the substances are further disintegrated or transformed in some other way, and, perhaps, even utilized for various syntheses. From this point of view we may look upon the lymph as a powerful means of defence, whose aid is particularly valuable in preventing the infusion into the blood of compounds that are both quantitatively and qualitatively unsuitable. From all sides care is taken that only normally suitable substances shall appear in the blood.
From this point of view we may distinguish substances that are "out of harmony with the body," i.e., such compounds as, in their structure and configuration, show no correspondence with the ​constitutent parts of the organism. To these belong all such substances as are received from the outside as nutriment, with the exception of those products which may be ranged amongst the most simple units, as, for instance, grape sugar. As substances "in harmony with the body," we would then term those which, when entirely recast, correspond in their structure to the essential composition of the particular species or individual. In addition to this general conception, which only means that a substance is not absolutely disharmonious to the body in general, we have undoubtedly to make a still finer distinction according to the special features of the compound in question. As early as the year 1906 we had suggested the advisability of distinguishing between substances which, though they are adapted to the blood, are nevertheless out of harmony with the varied cells of the body, and those which show any features characteristic of the structure of the cells of a particular organ. If our ideas concerning the structure of the particular cells of an organ, and the dependence of its functions on this peculiarity, prove correct, then it follows that, as we have already emphasized, each kind of cell must have at its disposal units of its own kind. We may then speak of substances that are "in harmony with" an organ, ​or even more precisely, "with the cells"; or "with the blood." Substances that are specifically elaborated for the blood would then be "out of harmony with" the cells, and conversely the substances "in harmony with" the cells are "out of harmony with" the blood, or better, with the plasma, because the components of the form elements of the blood are out of harmony with the plasma, and inversely. Products in harmony with the cells will only be in harmony with one another in so far as they belong to cells with similar functions, so that from this point of view, for instance, the specific elements of the thyroid gland must be regarded as out of harmony with those of the suprarenal bodies, and inversely. The idea of an entirely specific structure for each cell of an organ—both from the chemical and physical points of view—is based not only on the supposition that, without such a notion, the special duties and functions of the separate cells of the body would appear incomprehensible, but, above all, on the above-mentioned fact that definite secretions given off by particular organs act constantly and only upon cells of a definite system. This implies that the cells in question must have a structure which distinguishes them sharply from all other kinds of cells.
The view that each animal species is capable of building up complicated compounds of peculiar ​structure, and further, that every cell with special functions is formed of specially constructed components, is very often met with doubt. How is it possible for the animal and plant worlds to produce such an enormous number of different compounds? There would have to be formed millions and millions of different substances. Only think of the enormous amount of animal and plant species, and just put against this the fact that in general always the same and similar components reappear! In each cell we meet with carbohydrates, fatty substances, and albuminous particles. If these compounds are decomposed into their units, we find the same compounds resulting. All the albumens give, for instance, with very few exceptions, the same, that is, some twenty amino-acids. This obvious contradiction—on one side cell constituents based on similar elements, and on the other the idea of specifically constructed cells—disappears immediately we begin to make a calculation. Suppose we synthesize three elements A, B, and C; we at once obtain, by merely altering the sequence of the particular combinations, the following six different products:—
| A—B—C | B—A—C | C—A—B |
| A—C—B | B—C—A | C—B—A |
If we start with four different elements we get twenty-four different compounds, while five elements ​correspond to one hundred and twenty isomeric combinations. We give below the number of possible compounds which result from simply altering the sequence, the form of combination remaining the same.
| The number of different units | Number of resulting compounds, the sequence only being changed |
| 8 | 40,320 |
| 10 | 3,628,800 |
| 12 | 479,001,600 |
| 15 | 1,307,674,368,000 |
| 18 | 6,402,373,705,728,000 |
| 20 | 2,432,902,008,176,640,000 |
This enormous number of different compounds is solely produced by the manner in which the twenty elements follow one another. If hydrolysed, all these compounds would give the same elements to the same amount. These reflections may serve as a warning to those investigators who are inclined to infer the identity of particular compounds from the presence of the same elements.
Nor is it only the sequence of the individual units that needs to differ; for the mode of combination of the different compounds may also vary. The number of possible combinations is infinite. Again, the units are present in unequal quantities. Finally, one very important factor must be allowed for. No cell is composed of only one albumen particle, one carbohydrate, and one fatty substance; on the ​contrary, we always find mixtures of these. So that, given quite similar compounds, e.g., several albumens, the cell has the power of making up mixtures of various kinds which give it a special stamp. By these means we see then that the possibilities for the production of specifically constructed kinds of cells are infinite. No one would be able to calculate the number that would account for all these possibilities.
We take it as probable, on the strength of numerous observations, that all through the animal kingdom similar organs show, besides their specific, and possibly individual characters, certain features which are common to all species of animals. All that is required is the recurrence of a particular albumen in the cell. We conjecture this from the fact that experiments have shown that certain ferments, when they act on albumen of a special kind, show specificity for the organ, but yet are not specific for any particular animal species. It is probable that we are here on the track of an important biological law.
Yet, in spite of these similar or kindred features, each species and individual retains, by means of the mixing of its cell components, the cell organization peculiar to its kind. If a single group be repeated but once only, the ferment that acts on it finds a point of attack. We lay stress on these points, because a casual consideration of the fact that in the ​dialysation process, as well as in the optical method, human organs may sometimes be replaced by those of animals, might easily lead one to argue against the existence of specifically constructed cell units, as well as of the ferments that act on them.
A special place is occupied, at least qualitatively, by all those substances which, like the units of the different organic nutritive and tissue materials—as well as the inorganic constituents, the salts, water, &c.—exhibit no specific structure, and which are common to the most different kinds of cells, as well as to the blood and lymph, as intermediate and final products. In this case disturbances can only be caused by quantities. Rapid secretion, or synthetic or analytic processes, may in such cases act in a regulating manner and again restore normal conditions. All substances, however, which have a specific structure, are peculiar either to the blood or else to specific cells. From this point of view we must consider substances, which leave the cell and pass into the blood in a state of insufficient decomposition, as being out of harmony with the blood, or rather with the plasma; and, inversely, disturbances would certainly occur in the metabolism of certain cells, if, for instance, the insufficiently decomposed constituents of muscle cells were to penetrate the cells of the kidneys. The units of the muscle cells are out of harmony with the cells of the kidneys, and only a ​radical reconstruction could make them harmonious therewith.
That, in an animal organism, the formation of material for definite cells can be effected by the components of absolutely different cells, we can learn from experiments on the starvation of animals, and particularly from the well-known observations made by the Basle physiologist, Friedrich Miescher, on salmon. This observer was able to prove that the sexual glands of this fish become extraordinarily developed in fresh water at the expense of the muscles. It can be demonstrated microscopically that the components of the muscle tissues are gradually decomposed until they pass into the blood circulation; and Miescher speaks quite plainly of a liquidation of the units of the muscle cells. At the same time it may be observed that the sexual glands gradually begin to grow, without the animal taking anv nourishment. But in the cells of the sexual glands we do not meet with the specific muscular constituents in an unmodified state; on the contrary, we meet with quite new substances, chiefly albumens in a state in which they are never met with in the muscle cells. We notice in this case that histones appear in place of the muscle albumens. These are albuminous bodies of a basic nature, containing the so-called di-amino-acids in large quantities. Soon we find the histones, the more the sexual organs, and ​especially the testes, approach maturity, replaced by protamines, which consist nearly exclusively of di-amino-acids. We see, in this example, how cells of a characteristic structure transfer their material to the blood circulation in a profoundly modified form. First of all substances are produced that are in harmony with the plasma, and these are transferred to the cells of the sexual glands by means of the circulation. These glands take up the indifferent substances, and from them build up products specific to themselves. There is no doubt that similar processes play a part in normal metabolism. Sometimes one group of cells will help another in this way, particularly in cases where the supply of nourishment is delayed for some time.
The reconstruction of substances of every kind from products that are harmonious to the plasma and the lymph is demonstrated by every growing hair and every growing nail. Every new blood corpuscle tells us of far-reaching transformations; and every secretion—whether produced directly, as in the case of saliva or milk, or manifested when a fistula is produced by surgical means, or whether it forms a so-called internal secretion, choosing the blood or the lymph for its path of action—every one of these gives evidence of powerful disintegrations, integrations, or transformations. When thousands and thousands of leucocytes hurry forth against an invasion of ​micro-organisms, for the purpose of limiting their sphere of action or of subduing them, no more convincing picture could be presented to us of the synthesizing capacities of the animal organism. Even the full-grown organism is able at any moment to completely equip a vast army of cells and endow them with special functions.
If the ingested food materials, with their peculiarly disharmonious structure, were passed directly into the circulation and handed over to the cells in this state, then the organism would be subjected to continual surprises. The control of its metabolism would be utterly impossible under such conditions. Sometimes one substance, sometimes another, would predominate in the circulation, and the blood would be correspondingly affected sometimes in one way, sometimes in another. The cells would have to disintegrate all these disharmonious materials. In such a case they would have to be provided with all sorts of arrangements for the continual modification of these materials. Each separate cell of an organism would be in exactly the same state as a unicellular organism. Just as these have to make a selection from amongst the disharmonious substances by which they are continually bathed, so, too, would the cells of the body have to pick out the substances they need, according to the conditions presented. Not only would the work of the single cells be enormously ​increased, but also, without doubt, the mutual influence of different kinds of cells, by means of certain secretions, would be much hindered. And not infrequently we should find that some substance, that was quite specific in its structure, would be caught up by disharmonious substances circulating in the blood, and would be either altered or completely annihilated. In a short time the extraordinarily delicate regulation of the general metabolism would be thrown out of gear, and all kinds of injuries would inevitably result. The intermediate products in particular, which may vary in any given case, would give rise to disturbances.
The cell, as has already been mentioned, always works by degrees, for it is quite incapable of suddenly decomposing a complicated molecule, and of directly transforming it by means of combustion into its final products. The cell builds step by step, and so preserves the equilibrium of its energic metabolism. The rapid combustion of albumen, fats, and polysaccharides would, in certain places, suddenly produce a great deal of energy, which would appear in the form of heat, and under certain circumstances would destroy the life of the cell itself. In consequence, the gradual acquisition of the energic contents of the food is of the greatest value for the maintenance of all the finely graded processes of metabolism, as well as for the functions of the individual cell; while, on ​the other hand, the decomposition of some disharmonious, unsuitable, material may give rise to some intermediate stages which are the cause of serious disturbances. Here and there a cell would be seriously injured. Complete disintegration could never be effected, either because the cell would refuse to act, or because it would lack the particular agent with which to dissociate the compounds presented to it. All this would lead to numerous possibilities, which would exclude all regularity in the metabolism of the cells, as well as in the general metabolism of the body.
The animal organism prevents all these possibilities by allowing only material which has been put in harmony with the body, and particularly the plasma, to reach the circulation. The nutritive material of the tissue cells, which from this point of view can be considered homogeneous, gives decomposition stages with which the cells have been long familiar. Nothing that is disharmonious appears on the scene. Just as in a workshop, in the production of an article, one machine prepares the material for another, and one workman transfers to another material which is finished up to a certain degree, so do the tissue cells mutually support each other in their task. The cells of the gut and the liver continually act as important sorters for the whole organism. One may imagine the chaos and disturbance which would be ​produced in a workshop if machines were suddenly supplied with unsuitable material. All of them would soon refuse to work and come to a standstill. The single workman, who, with his knowledge and his tools, is trained only for a single phase in the production of a complicated whole, would be helpless if he were suddenly ordered to undertake a new task. He would require new tools, and be forced to acquire new experience. If his duties changed without any regularity at all, i.e., were he restricted in his activities to any casual work that might be given to him, then any successful results would be entirely out of the question. We find exactly the same relation in the collective mass of cells which compose our organism. The single cells represent the machines and the workmen who, in an enormous workshop, pursue common aims in separate groups. The cells of the gut and its accessory glands, especially those of the liver, superintend in a certain degree the supply of raw material, which is first prepared in a proper manner, and then recast so as to be "palatable" to all the cells; after which it passes from hand to hand—from one cell to another.
Tn these considerations it is not only the purely chemical processes that have to be taken into account; the physical processes also play an important rôle. Every cell possesses substances which have an ​influence upon osmotic pressure, together with others which are without this influence. In this respect, too, the cell is always laid down on the most delicate lines. Sometimes it decomposes colloidal substances and transforms them into others, which increase the osmotic pressure of the cell; at other times it synthesizes materials in solution into larger, more complicated molecules, until a body appears which is more and more extracted from the solution, and by this means loses its influence upon the osmotic pressure of the cell. This variety of function is of great importance to the cell in quite a different direction. We know that single ions exhibit very specific activities. Here also the cell must be equipped with arrangements to accelerate in one case the action of a separate ion and to check those of another, or else to entirely exclude them. The cell is able to effect this in diverse ways. Sometimes an ion is combined with a protein, for instance, or with other substances, and so is robbed of its own characteristics; at other times an ion is set free through decomposition or simple dissociation. Or else the cell induces antagonistically acting ions to react mutually on each other in finely graduated stages.
Numerous experiments have shown, as has already been mentioned, that definite cells depend upon definite secretions having their origin in other organs. If we remove certain organs, for instance the thyroid ​gland, the accessory thyroids, the sexual glands, the suprarenal bodies, and so on, we get definite degenerative phenomena appearing. In many instances, indeed, the absence of these organs is incompatible with life itself. The same phenomenon manifests itself when the organ is left in its proper place, but through some cause or other gradually discontinues its proper functions. In such cases there is no need for the organ to be destroyed; it is sufficient if the production of a specific secretion entirely ceases, a condition which is equivalent, to a certain extent, to the complete absence of the organ. These observations, which are supplied to us by pathology, together with facts which may be produced at any time—as when we extirpate certain organs and, after the results of such extirpation have manifested themselves, make a fresh transplantation—give an extremely varied picture of the reciprocal relations of the different organs towards each other.
Each group of cells—each organ—has certain functions to fufil in regard to the rest of the cell organization, and in this respect it possesses a certain independence of its own. There are also, of course, reciprocal relations within the cells themselves of an organ. Many observations point to the possibility that apparent morphological unity of an organ does not always mean unity of function. The independence of a given organ is only a relative one. As we have ​repeatedly indicated before, all the cells stand in actively reciprocal relations with each other. We have plenty of proofs for the acceptance of this view; while, on the other hand, we have no clear insight, at present, into the signification of this reciprocal dependence. Probably unicellular organisms alone are wholly dependent upon themselves. They perform all the processes necessary for life independently of other cells, except when, as sometimes happens, a conjunction of these simple organisms rises to the level of a symbiosis. The latter, as we have already pointed out, must have a value corresponding exactly to the reciprocal interactions of the cells of the more highly organized forms of the vegetable and animal kingdoms. For there is no doubt that in plants, too, the cells have actively reciprocal relations.
Doubtless there are, in an organism composed of cell groups, numerous kinds of cells which can live without having reciprocal relations with other cells, exactly in the same way as a single individual can isolate itself from its stock and still continue life for a certain time. But in the same manner as the well-being of a people or a State finally depends upon the regular collaboration of the many, so each kind of cell expresses its full value only by associating its work with that of the other cells in the organism. Only then is a cell capable of developing all its capacities. In many particular functions, indeed, ​so much division of labour is found, and to such an extent, that a large number of cells are entirely dependent upon the functions of others. Were such cells to cease to work this would result, as has already been mentioned, in the sickness and finally in the death of many other cells. In this direction there still lies an extensive field of research before us. The "whys" and the "wherefores" in this case extend indefinitely.
The possibility of breeding single cells and pieces of tissues in the blood plasma outside the organism, and keep them alive for a certain time, opens out a prospect of answering many problems by experimental means. We shall see in due course why some of the cells lose their normal functions when the secretion of certain organs is lacking. The number of possibilities is almost unlimited. For example, some substances, such as grape sugar, can only be dissociated by the cells into final products—carbon dioxide and water—after they have been prepared in a certain manner. A gradual dissociation takes place. The cell is equipped with appliances for the alteration of a given substance, but they are not at first in a condition suitable for use. A second agent must first of all make them capable of their respective functions—just as a hammer without a handle, or a screw without a screwdriver, are only useful when the missing parts are at our disposal. ​These agents are probably supplied by the cells of other organs.
It is quite probable that, at present, being too much concerned with the phenomena of structural chemistry, we observe the processes in the cell from a too one-sided point of view, and think too little of the physical state of the cell. We know that many reactions depend entirely upon the conditions present, if the action is to take place. For instance, a change in the reaction of the medium is sufficient to annihilate the activity of n ferment. The addition of the least trace of an electrolyte will, under certain circumstances, accelerate certain reactions; and alterations in the conditions may even upset a reaction entirely, and lead to totally different end products. The processes in the interior of the cells are surely subjected to a much greater extent to the influences of the physical state of the cell. Colloidal substances and electrolytes—the ions—and perhaps the rest of the substances in solution, certainly play a considerable rôle in their reciprocal relations. Here we meet with regulations of a kind which we are at present unable to discern. Might it not be in this direction that the collaborations of different body cells would appear of the greatest significance? Many a process, which manifests itself and attracts our attention most strongly on account of the ease with which it can be demonstrated, may perhaps be of quite a secondary ​nature. The cause—the primary process—escapes our notice, partly because at the time we do not know how best to state the problem, partly because we have no methods at our disposal for an experimental investigation of the case.
In all biological problems it is remarkable how entirely dependent we are upon the philosophy and the methods employed in the exact natural sciences. We transfer all that is there obtainable to the problems of biology. For some years certain ideas prevail, only to recede as soon as a new impulse or a new success in the domain of physics and chemistry directs a host of workers into new paths. We drill and work until a new gallery is driven into the rock of puzzles which is found in every cell. Very often the gallery ends blindly, but on its way has given rise to numerous interesting discoveries. Sometimes, however, the pioneer work is crowned with success. An important stage is left behind, and a new outlook gained. The final aim, however—a complete insight into the metabolism of the cell—still lies far ahead. Yet the knowledge we have acquired serves as a compass to keep us on the right road. The careful traveller will never leave anything unnoticed, for observations which often seem but trifles may point the way to entirely new problems.
In studying the functions of the cell we must never forget that there is not a single substance which is of ​no value to the cell. It would be quite erroneous if we were to consider any substance—for instance, albumen—as the paramount life substance. A single ion can in certain cases decide the life or death of a cell. An aggregation of molecules may combine to form a powerful complex—a colloid—and by means of its properties dominate the whole function of a cell. The structure and configuration of the separate compounds, and of the separate units of the cell are of the greatest importance for its individuality. To this we must add, and as partly conditioned by the above, their structure and configuration in the physical sense. A. separation of the chemical and physical properties of the cellular units is impossible, since they constitute mutually the conditions of life for the cell. They stamp it with its own character.
Substances, which may be indifferent products for one kind of cell, may be injurious to another kind. Each cell produces secretions of its own, in the formation of which many intermediate stages are passed through. If the whole transformation into substances that will be in harmony with the plasma be performed inside the cell, then any by-products that may appear, even though they be not indifferent in regard to other cells, will display no injurious activity in the organism as a whole. If, however, such insufficiently transformed substances penetrate into the general ​circulation, then we must expect troubles of all kinds. Such a case may arise, for instance, when certain cells cannot complete a decomposition that they have initiated, owing to the absence of the necessary agent, i.e., the ferment; so that the incomplete action of a particular organ may be the cause of numerous disturbances of every kind. If continuity of function be broken but once, then one disturbance, like an avalanche, is followed by another. It is true that the organism defends itself in such a case. It produces compensatory activities and tries to adapt itself to the new conditions, often succeeding in a most amazing fashion, and repairing the damage for a long period of time. Pathology supplies us every day with examples of this kind. The study of cellular functions under variable conditions is one of the most attractive that we know. Experimental pathology is a field which will be of undoubted importance for the whole of physiology, and to an extent as yet unrealized.
Thus all observations on the structure and metabolism of the individual cells of the body lead us, in the most unequivocal manner, to the conclusion that within a given organism large aggregates of cells work together harmoniouslv for the benefit of the whole. Complete harmony of relations is guaranteed—let us emphasize the fact once more—by ​having on the one hand the cells of the gut and the liver ready to prevent anything, that is not completely deprived of its own characteristics, from passing into the circulation, and, on the other hand, by having the cells of the body passing on to the blood only such substances as have been so far disintegrated as to have lost those features which harmonize them with the cells. Blood which is in circulation thus always shows the same metabolic products and the same substances; and from this point of view we may consider the contents of the blood as being always constant. No doubt the duty of the lymph, which is placed between the cells of the body and the blood, is to guard the blood against an excess of individual products of metabolism. Probably, also, some of the products, which have been insufficiently disintegrated, are finally decomposed by the lymphatic glands, or by the lymph itself.
We are bound in this sense to look upon the lymph system, as indeed we have already pointed out, as an important control station. By means of its own cells, and especially by means of the glands, the lymph watches that no material shall reach the blood which is out of harmony with it.
From the above point of view we gather an insight into the significance of the invasion of organisms of all kinds into an animal organism. The isolation of the whole organism is immediatelv disturbed when ​disharmonious cells settle on any spot within the hitherto harmonious cell complex. From this moment the harmoniously organized cells of the tissues are subjected to the influence of a kind of cell which has an utterly strange organization of its own. These new cells have a characteristic metabolism corresponding with their whole structure and configuration, and this they bring with them definitely into the new organism. They pass into the blood numerous end-products of their metabolism. Further, some cells decay here and there, and partial products reach the blood which are out of harmony with the species, and, of course, entirely so with the plasma and the cell. The whole regulation of tho normal metabolism is seriously injured. The cells of the gut-wall will still be on the watch to prevent any disharmonious material from entering the organism; and the single cells of the body will still struggle to supply the blood only with properly altered substances. But the whole organization has been damaged, in regard to the collaboration of its various cells, by the fact that disharmonious substances are continually given off by the invaders. The very same thing occurs if, through any cause whatsoever, the cells of the body change their structure and acquire a metabolism which is entirely foreign to the rest of the cells of the body. If cancer cells or sarcoma cells, for instance, appear, then we ​have cells before us which are neither subordinate to, nor co-ordinate with, the rest of the complex of cells. These cells have obviously reached a definite state of independence, nor do they maintain any direct relations with the different cells of the body. They are, so to say, outside the association of the cells of a particular organ, nor is there any doubt that they produce secretions, the products of their metabolism, which are out of harmony with the blood plasma. And we can well believe that here, too, cells decay, and products pass into the blood which are quite out of harmony with the plasma.
These ideas afford the possibility of studying, within the body, the action of disharmonious organisms of every description, especially of micro-organisms, and their relations towards the rest of the body cells, from a purely physiological point of view. It seems to us well worth while to follow up these conceptions, and to attempt, by means of direct experiments and observations, to bind together in closer relations the two fields of research that are covered by physiology and the study of immunity.
In the first place, we set ourselves the question: To what measures does an animal organism resort if substances penetrate into its body, and particularly into its blood, which are out of harmony with the species as a whole, or else only with the blood or ​plasma? Is it deprived of the possibility of defending itself against such substances, or have the cells of the body also, excluding those of the intestines, retained the capacity of attacking complicated substances which are out of harmony with the. organism, and of reducing them by profound decomposition to indifferent particles, which the cells may use for the construction of new material, or else as a source of energy?
To solve this problem, in a satisfactory manner, preliminary experiments on a very large scale were required. First of all, it was necessary to ascertain in what manner the individual cells of the body use up the nourishment which is normally brought to them by the blood. Does the individual cell decompose the complicated nutritive material directly into its end-products, or does it always disintegrate them first into simpler fragments, which are then reduced by successive stages, until finally the whole of the stored energy which the organism is capable of setting free is at the disposal of the cell, and the final products of the decomposition appear? All experiments that have hitherto been carried out in this direction lead us, as we pointed out at the beginning, to the idea that each separate cell of the body in general, with very few exceptions, disposes of the same, or of similar, ferments as those secreted by the digestive glands into the intestinal ​canal. These ferments may not be identical in all details. It is quite possible that the ferments passing from the glands of the intestinal canal differ more or less in nature, because, in the case of food, a much more heterogeneous mixture of separate products is introduced from the outside than is found in the already transformed nutritive material of the cells of the body, which circulates in the blood and lymph channels. It is also possible that differences prevail in the mode of disintegration, and consequently in the resulting decomposites. It is quite certain that the cells of the body are capable of hydrolytically splitting fats into alcohol and fatty acids. Further, they are able to decompose carbohydrates of a complicated structure, especially glycogen, through dextrines to maltoses. The maltose formed is reduced, by the ferment known as maltase, into two molecules of grape sugar. We know also that very dissimilar cells of the body contain ferments which decompose albumen into peptones. The latter are further reduced to still simpler products, and eventually amino-acids are left, which again may be subjected to further reductions.
It could, further, be easily shown that the cells of the body are able to decompose into their structural units the so-called polypeptides, that is, amino-acids linked in the manner of acid amides. These ferments have acquired the name of peptolytic ferments. Their ​presence has been demonstrated in animals and plants inside the most varied kinds of cells. In plants they are not always found in an active state. In seeds, for instance, they appear only when these are beginning to germinate. In the same way they are absent, as Iwanow has shown at my Institute, when plants are resting during the winter. In the fœtus their presence can be demonstrated fairly early. They can be detected, for instance, in a chicken on the seventh day of development, while in embryos of swine active peptolytic ferments appear on about the fortieth day.
The demonstration of the peptolytic ferments may be performed in various ways. One way is to treat them in the manner adopted by Edward Buchner, namely, to entirely destroy the cells of certain tissues or even single cells by trituration with quartz sand, so as to squeeze out the internal fluid of the cells. This fluid is afterwards mixed with kieselguhr, which readily absorbs moisture from the cell fragments, and produces a compressible plastic mass. The absorbed juice is then extracted out of the latter under pressure—up to 300 atmospheres—and filtered through a filter candle. We get a clear juice, which contains many components of the cells; the original structure of these having, of course, disappeared. In a juice obtained in this manner the presence of various ferment activities can be demonstrated, and it may be ​shown that many processes go on exactly in the same way, qualitatively, as if the cell were intact. But the principal life process, the oxidation to carbon dioxide and water, is not found. Even slight injuries to the cells are sufficient to annul this important process. In such a juice it may be said that only the preparative functions remain—all of them processes which we usually ascribe to ferments. If to the juice obtained in this manner a peptone containing very sparingly soluble amino-acids is added—as, for instance, tyrosin or cystin—or else a kind of peptone in the building up of which an amino-acid takes part—and this may be easily detected at the moment of decomposition by means of a colour reaction—then it is very easy to ascertain whether the juice contains any ferment that is capable of splitting the peptone in question. The precipitation of the respective amino-acids, or the appearance of the colour reaction, announces the presence of the decomposing agent.
Still more conclusive results are obtained if combinations of a known structure—for instance, polypeptides, in the building up of which the above-mentioned amino-acids take active part—be chosen for the experiment. Or one may follow the decomposition in a polariscope tube. A certain quantity of ​the expressed juice is mixed with a measured solution of an optically active polypeptide of known composition. The mixture is poured into a polariscope tube and the rotation for the solution is ascertained as quickly as possible. If one then determines the rotation from time to time, an insight into the nature of the decomposition is acquired. Instead of optically active polypeptides we can employ racemic bodies. The latter are optically inactive, because they consist of two halves equally strong as regards their respective rotations in opposite directions. The peptolytic ferments generally decompose only such polypeptides as are built up out of the optically active amino-acids as they are found in nature. If we have to deal with a racemic polypeptide, of which one-half complies with this condition, then this part is reduced to its component parts, and we are left with the other half of the racemic body, which consists of amino-acids not found in nature. We recognize this asymmetric splitting through the fact that the original optically inactive mixture becomes optically active.
An example may convey a clear idea of these conditions. In nature we meet the amino-acids l-leucin and d-alanin, while d-leucin and l-alanin have never yet been found amongst the products of reduction of the proteins. If we allow peptolytic ferments to act on the racemic bodies d-alanyl— ​l-leucin+l-alanyl—d-leucin, then we obtain the amino-acids l-leucin and d-alanin, and are left with the compound l-alanyl—d-leucin. This is optically active.
Most interesting results are obtained when optically active polypeptides are chosen for examination in the building up of which several amino-acids take part. As in these bodies the rotation of every possible reduction stage is well known, it is easy to find out, in the most exact and unequivocal manner, at what particular stage the peptolytic ferment of a particular tissue attacks the substrate employed. We have thus a means at hand of comparing ferments of different origins, together with the possibility of recognizing, in the most exact way, all the specifically active peptolytic ferments. Further development of this field of research, by the use of the greatest variety of substrates from all kinds of substances, is required, in order to give an answer to the question of the peculiarities of certain kinds of cells in many directions. It will be possible in future to recognize certain cells by the manner in which they reduce substrates, the synthesis of which, as a matter of course, must be previously fully known to us.
An example will make clear this method of studying cell ferments. The subjoined scheme supplies ​ information on the power of rotation of three poly-peptides composed of three amino-acids. At the same time the optical relations of the individual decomposites are given.
Finally, we may, for the purpose of tracing peptolytic ferments in tissues, inject into the tissues peptones and polypeptides, which contain sparingly soluble amino-acids, and observe directly whether any amino-acids are set free.
In all these experiments the co-operation of micro-organisms was most carefully excluded, and there can be no doubt that these ferments belong to the tissues themselves. The same holds for ferments ​that act on fats, carbohydrates, nucleo-proteids, nucleic-acids, phosphatides, and so on. Everything points to the fact that the cell has agents at its disposal which render it capable of splitting up, into their simplest units, all the complicated substances which are brought to it, or which it itself builds up. In favour of such a view, we may more particularly cite, besides the direct proof of the existence of ferments, the observation that in the metabolism of the cell all the units, out of which the complicated nutritive substances and the components of the cells are built up, are found to occur.
At the present time there is no doubt that an important part of the metabolic processes of the cells is furthered by ferments. In general, we may say that complicated substances are hydrolytically reduced in stages until the simplest structural units are formed. Once the latter appear, then the further reduction continues in stages, through various intermediate products, right down to the end-products of metabolism, or else the resulting products of decomposition form the starting-point for new syntheses. From these products very varied links are forged between very different groups of substances.
It is thus proved that, in a certain sense, each separate cell of the body is capable of digestion. This holds particularly for the white and red blood corpuscles; even the platelets are able to produce ​hydrolytic decompositions. The blood plasma is unable, either in the majority of animals or in man, to produce decomposition of albumens, peptones, and polypeptides, at least not in any degree which can be demonstrated by available methods. The capacity for decomposing fats is also apparently absent in most cases. On the other hand, we often meet with assertions that the blood always has a diastatic action, i.e., the capacity for splitting complicated carbohydrates. Under normal conditions the blood plasma does not generally seem to be constructed for the reduction of complicated substances. Only in the l case of guinea-pigs do we find conditions that are undoubtedly exceptional; here the blood plasma shows other properties, and even under normal conditions can partly break down polypeptides which are not in the least acted upon by the blood plasma of other animals. The cause of this peculiar behaviour of the plasma in guinea-pigs cannot yet be explained. That the blood plasma in general is lacking in digestive powers must obviously be construed in the sense that, under normal conditions, substances which are out of harmony with the plasma, and require a quick chemical reduction, never have access to the blood.
As soon as these observations had been made it become possible to study the question, whether the blood plasma exhibits new properties in cases where substances that are out of harmony with the plasma, ​and particularly with the body, find their way into the plasma of an organism by any other way than through the intestinal canal. The order of these experiments was of the following character:—
In the first place we determined the composition of the blood plasma, or of the serum, in an animal, in regard to the proteolytic and peptolytic ferments it contained under normal conditions, that is to say, when the nourishment is normal. The manner in which this is done is as follows: 10 c.c. of blood is taken from the animal under experiment, for instance, from a dog, from the vena jugularis externa or from a vein of the leg. Either this is left to clot of its own accord, so as to separate out the serum ; or else 0.1 gr. of ammonium oxalate is added to the test-tube containing the blood, so as to prevent it from clotting. The form-elements are centrifuged out, and the clear plasma can then be withdrawn easily by means of a pipette. In both cases—serum and plasma—we must test for the absence of hæmoglobin, for, if it is present, then the red blood corpuscles have been broken up, in which case we may be quite certain that the ferments belonging to the red corpuscles have passed into the fluid derived from the blood. Only serum and plasma which are absolutely free from hæmoglobin must be used for these experiments. To a measured quantity of serum or plasma a certain quantity, in cubic centimetres, of ​an albumen, peptone, or polypeptide solution, having a known composition in regard to substrates, is added; a polariscope tube is filled with the mixture, and the rotation is quickly ascertained by means of a good polariscope. The tube is then placed in an incubator, and from time to time the angle of rotation is again noted. To avoid mistakes another tube is filled with the same quantity of plasma or serum, and normal salt solution is added in the same quantity as the substrate solution employed; this mixture is then observed in the polariscope under the same conditions as the former. Finally, another test, with the substrate solution alone, is arranged in the same way. It is further essential to add to the mixture a measured quantity of a phosphate mixture for the purpose of preventing the action of the ferment from being in anv wav influenced bv changes in the reaction of the mixture. To prevent cooling of the polariscope tube its jacket is filled with water at 37° C., or an incubator is used, which can be fitted to the polariscope (see below, the technique of the optical method). Decomposition of proteins or peptones could never be observed in these experiments, so long as the blood was taken from healthy, normally fed animals.
We now take the animal under observation, i.e., the animal whose plasma or serum we are investigating, and introduce selected substances directly ​into the organism, so as artificially to avoid the disintegrating action of the ferments of the intestines. These substances are injected either subcutaneously, or into the abdominal cavity, or else intravenously. After a certain lapse of time blood is extracted, and its serum, or plasma, is treated exactly in the same way as we have described above.
The first experiments were made with dogs and rabbits. White of egg, or horse blood-serum, was introduced parenterally into these animals, that is to say, avoiding the intestinal canal; tests were then made to see whether the plasma of the animals under experiment either decomposed certain polypeptides, or whether it decomposed them quicker than the plasma of the same animal did before the injection of the disharmonious substance. The very first experiments gave a positive result. It was found that the contents of the blood increased in peptolytic ferments. In a further experiment the substance used for the injections was silk-peptone. It was found that the serum of normal rabbits did not reduce this peptone at all, the angle of rotation of the mixture of plasma + peptone remaining constant. But if silk-peptone be injected into an animal, and the serum of the latter be then brought into contact with this peptone, then, if we take a rapid reading of the rotation in a polariscope, we find that the initial rotation alters in the course of time.
​Experiments were then made with gliadin and with peptones obtained from gelatine, from edestin, and from casein. Edestin and casein were also injected by themselves. In all cases the result was the same. When substances, that are out of harmony with the plasma, are introduced into the plasma or serum of a given animal, we always find developed a special power of decomposing bodies belonging to the protein series, especially protein itself and its peptones. A specific activity of the injected substrates could be traced only so far as that, after the injection of proteins and peptones, ferments appeared in the plasma which were able to chemically reduce the derivatives of this group, but not, for instance, fats or carbohydrates. Conversely, no splitting of protein could be traced after injections of fats, of carbohydrates, or of amino-acids. On the other hand, after injection of a particular protein, or of a particular peptone mixture derived from a definite protein, not only were the injected substances decomposed by the plasma, but the decomposition extended to the whole group of proteins and their nearest derivatives.
That the process actually depends upon the presence of ferments can be proved in two ways. In the first place the splitting of a particular peptone solution, by the plasma of suitably prepared animals, was compared with the action of extracted yeast ​juice on the same peptone. It was possible to show that the decomposition in both cases was very similar, i.e., that the initial rotation varied in the same direction and to the same extent, whether the plasma of specially treated animals was used, or the active extract of yeast.
The following experiment proved, with exceptional clearness, that the plasma of an animal, when specially treated, actually reduces proteins. The plasma was mixed with gelatine or with white of egg, and the mixture was placed in a dialysation tube. Very shortly the presence of peptones could be demonstrated in the outer fluid—distilled water being chosen for this purpose—by means of the biuret reaction. But when plasma of normal animals was mixed with albuminous bodies and placed in a dialysation tube, no substances giving the biuret reactions could be traced in the outer fluid, even after standing for many days. Finally, it has been proved quite recently that, by mixing the plasma or serum of specially treated animals with albumen, the nitrogenous contents of the outer fluid increase to a considerably greater extent than when the plasma of normal animals and albumen are mixed together. In the last case the increase of nitrogen in the outer fluid is no greater than when the same quantity of plasma is brought into the dialysation tube by itself, i.e., without addition of albumen. It must be understood ​that, in this experiment, the albumen has to be previously freed from all nitrogenous and crystalloid admixtures by dialysis or by boiling.
When the plasma of specially treated animals, which experiment showed to be active, that is, to split up proteins and peptones, was raised to the temperature of 60°C. it became inactive, i.e., its decomposing action could no longer be demonstrated.
The facts we have enumerated have been repeatedly verified by numerous experiments. In all these experiments on specially prepared plasma or serum control experiments have, of course, been carried out, on the one hand with peptone solutions alone, on the other hand with the plasma alone. Further, the serum, or plasma, was made inactive each time, for the purpose of avoiding any error, by raising the temperature to 60°C. Finally it was shown, by the use of the dialysation method, that the observations made by means of the so-called optical method were absolutely correct. It mav also be mentioned that iodized albuminous substances were also injected, and that no splitting action of the blood plasma could be produced in this case. We know, from other experiments, that iodized albuminous substances are decomposed with difficulty or not at all. It seems likely that they are so intensely disharmonious with the body that the organism, even though armed with the proper ferments, can find no ​point of attack from which to initiate their decomposition.
Some examples which, in the form of curves, represent the results obtained from the disintegration of mixtures of plasma, or serum, with some substrate (albumen or peptone), may serve to illustrate the above statements.
(1) A dog, whose serum did not decompose peptones, was given 0.5 gr. of casein by means of a subcutaneous injection on November 25 and 29 and December 4. The blood used in the experiment below was withdrawn on December 6. The polariscope tube was filled with a mixture of 0.5 c.c. of serum, 0.5 c.c. of silk-peptone solution (10 per cent.), and 7 c.c. of normal salt solution (see fig. 1).
Fig. 1.
(2) A dog was given repeated subcutaneous injections of crystallized albumen obtained from seeds of the gourd. The last injection was made on December 8, 8 gr. of albumen being injected. The serum was examined on the following day. For this experiment 1 c.c. of serum was mixed with 0.5 c.c. ​of a 10 per cent. gelatine-peptone solution, and 2.5 c.c. of normal salt solution (see fig. 2).
Fig. 2.
(3) The dog in this experiment was given on October 18, 3 c.c. of a 10 per cent. silk-peptone solution by subcutaneous injection. On October 21 blood was taken. The serum split up both silk-peptone (curve a in fig. 3), and gelatine (curve c in fig. 3). At a temperature of 60°C. the serum became inactive (curve b in fig. 3).
We may point out here that we thought it possible, at first, that the phenomena observed by us might have some connection with what is called anaphylaxy, or supersensibility. By this we understand the ​extraordinary property possessed by the animal organism of responding with certain typical symptoms to a second injection of the same material as was used in the first injection. A certain time elapses—in the case of a guinea-pig, about fifteen to twenty days—before this state is overcome.
Fig. 3.
(a) 1 c.c serum.
    0.5 c.c. of a 10 per cent. silk-peptone solution.
    5 c.c. normal salt solution.
(b) 1 c.c. serum at a temperature of 60º.
    5 c.c normal salt solution.
(c) 1 c.c serum.
    1 c.c of a 1 per cent. gelatine solution.
    4.4 c.c normal salt solution.
Cramp can be observed within different groups of muscles, as well as a sudden fall of temperature, &c. Peptones also can be demonstrated in the blood after reinjection of the original protein. Various authors have supposed that anaphylaxy is directly connected with the production of derivatives of proteins, particularly peptones, without, however, having ​succeeded in supplying definite proofs for such a view. It is only recently that experiments have been made, by means of injections of peptones and derivatives of amino-acids, especially of amines, with a view to producing phenomena resembling those of an anaphylactic shock. It is difficult to decide with any certainty what part is played, by the ferments we have observed, in the setting up of anaphylaxy. Several facts run counter to the supposition of a direct relation between the presence of active ferments and the particular substrate against which they are directed. It has been proved, beyond doubt, that these ferments exist in the blood at a time when the anaphylactic shock cannot yet be produced by a second injection of the same material as was used in the first case. Further, it has already been pointed out that these ferments are specific only in respect of the group of substances which are used for the injection, but not for the particular body that has been introduced. To produce the shock, on the contrary, the substrate, with which the animal under experiment was rendered sensitive, must be present. A certain importance, in regard to the setting up of the state of shock, may be attached to the power possessed by the plasma of decomposing albumen; as is shown by an observation which was made by Hermann Pfeiffer and confirmed by ourselves, according to which the proteolysis in the plasma disappears during the ​moments following the anaphylactic shock, i.e., during so-called antianaphylaxy—a state in which the animal becomes absolutely insensitive towards further injection.
If we summarize all the results obtained up to date, we arrive at the conclusion that our observations with regard to the appearance of ferments in the blood plasma, after injection of disharmonious proteins and peptones, undoubtedly stand in some kind of relation to anaphylaxv. The special significance of these ferments, however, remains uncertain. It would appear possible that these ferments acquire some special properties in the course of time, and then, by decomposition of the second dose of albumen, give rise to derivatives of a highly specialized nature and activities.
There are many other possibilities to be considered. The decomposition may not necessarily take place only in the blood. Our method has at present only demonstrated the appearance of ferments in the plasma or serum, and that could only be done because the ferments, which we find after parenteral introduction of proteins and peptones, cannot normally be traced in the blood plasma of certain animals. It is not unlikely that, after the introduction ​of substances out of harmony with the species, new properties appear also in the cells of the body, and that the latter undertake likewise the decomposition of these disharmonious substances. In a certain sense each individual cell would act in the presence of the disharmonious material exactly in the same way as an unicellular organism, and fight them to the extent with which it is provided with the necessary weapons—the ferments—that enable it to make a successful attack on the substrate. Like primitive organisms, too, it is able to protect itself against the penetration of these substrates by means of the constitution and quality of its walls, and so to wait until the modification of the substances has been effected elsewhere to such a degree, that all their disharmonious properties have disappeared, and only an indifferent product remains.
Finally, it may be that the whole problem of anaphylaxy will not be resolved by purely chemical considerations only. Why should not disturbances originating from dislocations of osmotic equilibrium, or activities of special ions, be taken into account, and associated with the other observed phenomena. (Cf. on this point Lit. 13.)
The more widely the limits of these problems are extended, the more probable does it become that the experimental testing of all possibilities will put us on the proper road for an explanation of the phenomena ​observed. Surely it would be absurd to limit the study of anaphylaxy only to a study of the behaviour of the blood; for it is more than likely that it is the cells of the body which ultimately play the chief part in the appearance of anaphylaxy. The behaviour of the blood plasma is possibly only a reflection of the defensive measures adopted by the cells of the body; while, in any given case, it may be only a special type of cell that has to be considered.
Special interest attaches to the proof of how the organism reacts when blood of its own kind, or from another animal species, is introduced into its circulation. In the latter case ferments appeared in the plasma, which decomposed albumens and peptones. If harmonious blood were chosen from an animal of the same race, no reaction whatever was noticed when it was transmitted directly, i.e., without leaving the blood-vessels. When, on the contrary, blood which belonged to an entirely different race was introduced into a dog, then a decomposition could be demonstrated within the circulation.
Against the results thus obtained one might raise the objection that the appearance in the circulation of active reducing ferments would give rise to enormous disturbances, because even those albuminous bodies that are in harmony with the plasma are liable to be attacked by them. But this is evidently not the case, since the plasma, though containing an ​active ferment, retains its initial angle of rotation; and it is only in very exceptional cases that dialysis shows the presence, in the outer fluid, of substances that give the biuret reaction. It is only after proteins or peptones are added to the plasma, that the activity of the ferments first manifests itself.
How can we explain a behaviour that is, a priori, so peculiar? There are already, before the addition of the proteins or peptones, large quantities of albumen in the plasma in the presence of an active ferment. We must always remember, in this connection, that the ferments are directed, in a more or less explicitly specific manner, against certain substrates. A slight alteration in structure and configuration suffices to remove a substrate from the influence of a given ferment. Just as the ferments themselves are first transformed into their active form by means of a special agent, so, without doubt, the substances in the blood and the cells which are presented to the ferments need special agents to bring them into a condition suitable for attack.
The substrates, too, are rendered active in a certain sense. The body defends its cells, and the substances contained in them, against disintegration by ferments by giving them a structure and configuration—it may be that their physical condition also plays a part—which are out of harmony with the ferments; and from this point of view we can understand why ​the harmonious proteins of the plasma are not attacked by the ferments which circulate in the blood.
Finally, the question may be raised, why the decomposition of parenterally introduced proteins and peptones cannot be followed up directly, by observations on the rotating power of the plasma, without the addition of proteins or peptones. If the appearance of proteo- and peptolytic ferments in the plasma has the object of undertaking the decomposition of the substrates introduced into it, then we ought to be able to follow up the digestion—the decomposition—in the plasma itself. As a matter of fact it has been found possible to demonstrate, by means of intravenous introduction of large quantities of proteins and peptones, after the animals have been prepared by previous injections, that, when the blood is withdrawn immediately, not only has an alteration taken place in the original rotation of the plasma, to which nothing has been added, but also that peptones may be found in the outer fluid in the dialysation test. That this demonstration does not generally succeed—i.e., that the decomposition of the substances that are out of harmony with the body cannot be followed up by means of observations on the plasma alone, without the addition of substrates—depends primarily upon the fact, that the injected substances suddenly become ​very much diluted, and then probably pass straight into the lymph, and possibly also into the cells of the body. The optical method is not so exact as to permit us to establish very minute changes in rotation, and, even if it were possible to observe such rotations, it would be impossible to know for certain whether the fluctuations were not within the limits of errors of observation. Moreover, the decomposition undoubtedly proceeds quickly, so much so that we are really indebted to a lucky chance when we are able to follow up the decomposition of the injected matter in the plasma itself. These are the reasons why we have to prove the presence of the ferments by means of substrates, against which the respective ferments are directed. The substrate is the reactive for its corresponding ferment, and the decomposition of the former betrays the presence of the latter.
It may be remarked that the clear establishment of the presence of proteo- and peptolytic ferments in the blood plasma, after injection into the circulation of albuminous substances that are out of harmony with the body, has supplied a real explanation of the behaviour of parenterally injected proteins during metabolism. There is no longer any doubt that they are made use of, that is, that they are utilized in the metabolism of the cells of the body, so far as experience has shown decomposition to be ​possible. Different observers (Lit. 4, 8, 10, 11, 12, 16, 17, 18, 19), who have instituted experiments on metabolism subsequent to parenteral introduction of proteins, have suggested that decomposition by means of ferments takes place outside the intestines. This is most clearly stated by Heilner. This suggestion, however, was only proved by the direct demonstration of the ferments by means of the experiments and methods we have described.
The positive knowledge that it is possible to induce a splitting activity in the blood plasma of animals, the plasma of which is otherwise unable to decompose albuminous substances, by means of parenteral injections of these substances, led of itself to the problem whether analogous phenomena appear when other substances, which are out of harmony with the body and the plasma, but do not belong to the albumens, are used in such injections. We began with the parenteral introduction of disharmonious forms of sugar. In the first place it was ascertained that the plasma or serum of dogs is unable to split up cane sugar. If blood serum, or blood plasma, of a dog be brought into a solution of cane sugar, it can easily be demonstrated, by means of analytical methods, that the cane sugar does not undergo any alteration. Certainly no decomposition takes place. The contents of the blood plasma are not increased in respect of reduced substances. If, ​however, in this experiment we use the blood plasma, or serum, of a dog to which cane sugar has been administered as an injection, either subcutaneously or directly into the circulation. then, on bringing this plasma and cane sugar together. we observe that the reducing potentialities of the mixture are considerably increased. Simultaneously, it is possible to show that the quantity of the admixed cane sugar diminishes.
These experiments give very positive results when the splitting action of the plasma is investigated with the aid of the optical method. in this case plasma is taken from a normal dog in a certain quantity, and a known amount of cane sugar solution is added: a polarization tube is ﬁlled with the mixture, and the rotation of the latter is ascertained. The readings of the polariscope are taken from time to time, and the tube is kept during the intervals in an incubator at 37° C. It is found that the initial rotation keeps constant.
Now. if an injection of cane sugar is made into the circulation of the same dog from which the plasma was taken. it may be demonstrated after a very short time that its plasma is now capable of breaking up cane sugar. The strong rotation to the right, which we observe at ﬁrst. decreases continuously. It approaches zero, and ﬁnally, passing zero, it travels to the left. We obtain eventually a left-handed ​rotation, the cane sugar being converted into invert sugar. The, latter consists of one molecule of grape sugar and one molecule of fruit sugar; that is, of the units of the disaccharide, cane sugar. Since the fruit sugar turns more to the left than the grape sugar does to the right a ﬁnal rotation results to the left. Many observations point to the fact that, at the same time, part of the products of the decomposition suffer further disintegration.
Parenteral introduction of cane sugar does not always succeed in effecting the appearance of invertin in the blood plasma. Obviously, the time during which the disharmonious substance remains in the blood plays an important part in the formation of the defensive ferments. The cane sugar is very quickly excreted through the kidneys.
The following examples will give an idea of the results of these experiments:—
(I) A dog was given subcutaneous injections of cane sugar (5 gr. at a time) on October 22 and 23. The blood taken on October 24 was used for testing ​the behaviour of the serum towards cane sugar. To 1 c.c. of serum was added 1 c.c. of a 10 per cent. solution of cane sugar and 5 c.c. of normal salt solution. The initial rotation of the mixture was + 0.45°. At the end of the experiment the rotation had sunk to - 0.50° (see fig. 4).
(2) Blood was taken from a dog before the parenteral introduction of cane sugar. and the behaviour of
Fig. 4.
the serum towards this disaccharide was ascertained. Decomposition did not take place (curve 1 in fig. 5). Then 10 c.c. of a 5 per cent. solution of cane sugar were given to the animal by intravenous injection. The sample of blood, taken fifteen minutes after the injection, already showed hydrolysis of the cane sugar that had been added (curve 2 in fig. 5). For the purpose of control the rotation of the serum without the ​addition of cane sugar was noted (curves A and B in fig. 5). The arrangement of the experiment is shown in the following summary:—
    (1) 0.5 c.c. serum (blood taken before the injection of cane sugar).
       0.5 c.c. of a 5 per cent. solution of cane sugar.
       7 c.c. normal salt solution.
Fig. 5.
    (2) 0.5 c.c. serum (blood taken fifteen minutes after intravenous injection of a solution of cane sugar).
       0.5 c.c. of a 5 per cent. solution of cane sugar.
       7 c.c. normal salt solution.
       A and B. 0.5 c.c. serum.
             7.5 c.c. normal salt solution.
    (3) Further experiments were undertaken for the ​purpose of studying the question, how long after the actual parenteral introduction of cane sugar the presence of invertin in the blood serum may be demonstrated. After a single subcutaneous injection of cane sugar the power of decomposing this disaccharide was still traceable at the end of fourteen days (curve I in fig. 6). In a dog, which received a
Fig. 6.
subcutaneous injection of cane sugar on two occasions, it was still possible to bring about an energetic splitting of this disaccharide with blood serum after nineteen days (curve II in fig. 6). The property once acquired does not therefore disappear at once. The individual experiments were conducted with the ​following quantities of serum and cane sugar solution:—
| (1) | 0.5 c.c. serum (blood taken fourteen days after injection of cane sugar). |
| | 0.5 c.c. of a 10 per cent. solution of cane sugar. |
| | 7 c.c. normal salt solution. |
| (2) | 0.5 c.c. serum (blood taken nineteen days after the second injection of cane sugar). |
| | 0.5 c.c. of a 10 per cent. solution of cane sugar. |
| | 7 c.c. normal salt solution. |
Control Test.
| A and B. | 0.5 c.c. serum. |
| | 7.5 c.c. normal salt solution. |
These results, without our knowing it, confirmed experiments which Weinland had made before us. He had already been able to show that the blood plasma of a dog is able to split up cane sugar; that is to say, it contains invertin as soon as cane sugar is parenterally introduced. These experiments were then later extended to other kinds of sugar, and especially to milk sugar. It was possible to show that the latter also undergoes alteration, but it seems that here, alongside of a hydrolysis, a decomposition takes place in another direction.
Very extraordinary is the observation that, after the introduction of soluble starch, and also of milk sugar, the blood plasma or serum is able to decompose ​cane sugar. It seems as if here also, after the introduction of a disharmonious kind of sugar, ferments appear which are not exclusively directed against the carbohydrate injected. Further, the ability of the organism to supply ferments seems to have limits, because, after an injection with raffinose, no definite reaction could be traced. Very likely this material is too markedly disharmonious with the cells of the body.
It is interesting to note that ferments contained in the plasma persist for a long time after the introduction of disharmonious substances, whether they be products of the albumen order or of the carbohydrates. The splitting activity of the plasma could still be clearly traced in individual cases up to three weeks after the injection. Important, too, is the fact that, after an intravenous injection of cane sugar, invertin could be demonstrated in the blood plasma within a quarter of an hour. When albuminous substances were introduced subcutaneously, then three to four days elapsed before the formation of the ferments attained its full value. After intravenous injections they manifest themselves within twenty-four hours. The fact that there are individual differences is also important. Moreover, the appearance of the defensive ferments is very much delayed after the introduction in large quantities of substances out of harmony with the blood.
​Finally, the behaviour of fatty products was tested. In this case difficulties of method were encountered at first. The experiment made to ascertain the decomposition of fat in the blood, by simple titration of the acids produced, failed entirely. The question, whether, after the introduction of fats that are out of harmony with the body and the plasma, an increase follows of the amount of lipase in the plasma, could only be attacked after Michaelis and Rona had selected the alteration of surface-tension during dissociation as the basis of a method for the study of the decomposition of fats. The fats belong to a group of substances that are strongly surface-active, while the products of disintegration produced by their decomposition, such as alcohol and fatty acids, possess no marked influence over surface-tension. If plasma of a normal animal be mixed with any kind of fat, such as tributyrin, and the mixture be allowed to flow from a capillary tube, a certain number of drops escape in a given time. But if any fat gets into the animal's circulation by whatever means, then the number of drops escaping through the capillary tube decreases.
As far as we can judge from the experience gained up to the present, it seems that the conditions met with in fats are much more complicated than in the case of proteins and polysaccharides. This experience tells us that while, under normal conditions, ​proteins of a definite kind, and in obviously definite quantities, are always circulating in the blood, and the amount of carbohydrates also varies only within narrow limits, the fats behave quite differently. The amount of fats in the plasma varies within a wide range. After a meal rich in fat we find so much fat in the blood plasma that it may be seen with the naked eye; and, if we let the plasma stand, the fat separates out directly and appears as a layer on the surface of the plasma. A short time after the meal the fat disappears again from the blood. It is transmitted to the different cells of the body, and is there used up, transformed, or even directly stored as reserve material. It seems that the blood, with every increase in the amount of fat, responds with an increase of lipase. From the point of view we have laid down the excess of fat has to be considered as being out of harmony with the plasma. Only in an animal whose stomach is completely empty do we find no, or very little, capacity for splitting fats. After a meal rich in fat active lipase can be demonstrated in the blood. It can also be shown that during a more or less prolonged hunger period the splitting power of the blood increases. This corresponds with the experience that, during fasting, an active transportation of material is going on. In many cases of fasting large quantities of fat could be shown to be present in the blood. If a fat be introduced that is ​out of harmony with the species, we find in the plasma an exceedingly high capacity for splitting fats.
In the case of fats we meet with some difficulties when we try to introduce, into the circulation, fats that have not been modified so as to be in harmony with the plasma. If they are injected subcutaneously they remain at the point of injection for a long while, and are probably only transported further after the actual splitting has begun. In cases of intravenous injection one runs the risk of killing the animal, owing to fatty embolisms. The introduction, into the blood, of a fat that is out of harmony with the species could only be effected for the first time after an old experiment of J. Munk had been made use of, namely, to gorge an animal with an excessive quantity of fat, so that it may easily be demonstrated in the tissues and, naturally, also in the blood. We fed in this way on large quantities of rapeseed oil and mutton suet, and then found in the plasma a very strongly marked capacity for splitting fats. We may mention here, also, that the same effects may be produced, with proteins and peptones, and also with carbohydrates, as in the case of parenteral injection, if an excess of these substances is forced through the intestines bv flooding the intestinal canal with the particular nutriment. We would also emphasize the fact that a state of anaphylaxy may be successfully set up by this means. If we ​introduce into an animal a large amount of white of egg, there is no doubt that unaltered protein passes into the circulation. It is also possible that peptones are absorbed, which still have the specific structure of the white of egg. This transfer may be ascertained by the so-called biological reactions, precipitin reaction, &c., but chiefly and most exactly by demonstration of the existence of peptolytic ferments in the circulation. If, after a certain interval, white of egg is once more introduced by either parenteral or enteral means—in the latter case the supply must be very copious—the state of shock is obtained.
Seeing that harmonious fats, as we have already mentioned, also produce in the circulation an increased power of splitting fats, it is rather difficult to determine whether disharmonious fatty products give rise to a definite specific activity. Further experiments will be needed to determine this point.
Finally, we have also made injections of nucleo-proteids, nucleins, and nucleic acids, introducing them into the organism in such a way as to prevent them passing through the intestine. We found that, after introduction of these bodies, ferments appear in the blood plasma in increased quantity, and quickly reduce these substances (see also Lit. 21). Moreover, it could be shown that it was possible, by means of ​certain nucleo-proteids as well as nucleins, to excite anaphylactic phenomena of a very specific character. Experiments on guinea-pigs, which were made in collaboration with Kashiwado, showed that a second injection of the same substance as was used in the first instance produced specific cramps of the muscles of the neck and of the jaw. Moreover, an increased peristalsis was regularly present, the animals excreting faeces continuously. Symptoms of lameness soon set in, and a marked fall of temperature always took place. We injected, for instance, nucleo-proteids, nuclein substances which had been obtained from the thymus, and finally nucleo-proteids from the blood corpuscles of a goose; the reaction was in all cases a strictly specific one. In the case of nucleic acids we were unable to get definite results, and it would appear that these cannot produce anaphylactic phenomena. It may be that, in the nucleo-proteids and in the nucleins, their albuminous components are the deciding factor. A systematic study of the nuclear structure of the various cells of the same individual may enable us to determine the question, whether albumens that are in harmony with the nucleus take part in its construction, or whether the nucleus plays a part, in the cellular metabolism, which is repeated in an identical manner in the various cells of the same individual.
So long as purely chemical research is unable to ​answer questions concerning the finer structure of the cell elements, we are bound to resort to indirect methods. The latter have, in a relatively short time, opened up a vast field, and discovered views of the widest interest in regard to every kind of cellular process. It is the duty of the future to follow up with exact methods all the observations that have been made, and to replace with known quantities the many unknowns with which our present-day methods have still to reckon.
* ↑ The numbers refer to the Bibliography given at the end of the book.
* ↑ See in connection with this, Emil Abderhalden, "Synthese der Zellbausteine in Pflanze und Tier," Julius Springer. Berlin, 1912.
* ↑ If the nitrogenous basis from which different microorganisms obtain their nourishment is not known, it might be possible to obtain a culture medium by decomposition of the micro-organisms themselves.
* ↑ A firm at Hochst a/M. supplies peptones of definite composition for this purpose.
* ↑ From this point of view it is easy to see why lack of its proper milk sets up disturbances in the suckling, and particularly how dangerous are continual changes in the composition of the food, seeing that the young animal is not yet prepared for the reception of mixed nutriment.
* ↑ "Lehrbuch der physiologischen Chemie," I Auflage,. S. 292, Urban and Schwarzenberg. Berlin-Wien, 1906.
* ↑ This is the case, for instance, with tryptophane.
* ↑ Here we have an enormous field, promising very fruitful results with respect to the most varied problems connected with the chemistry of albumen, with studies in immunity, with bacteriology, and so on, but which fails simply through lack of means for the upkeep of a small army of capable young chemists.
* ↑ Hermann Pfeiffer, of Graz, at about the same time as, and independently of, ourselves, has demonstrated the existence of proteolytic ferments in the blood plasma of sensitized animals, after we had already established the fact of the appearance of peptolytic ferments subsequent to the introduction into the blood of disharmonious derivatives of albumen, and had in this way systematically treated the whole problem. The first experiments were made with albumen. They have since been abandoned, because the results of an alteration in rotation seemed particularly ambiguous in cases where the serum of animals, treated previously with albumen, was brought into contact with albumen or peptone. For this reason polypeptides are preferable for reactions on ferments, as being compounds whose exact structure is known to us.
* ↑ Other substrates, which are also decomposed, may not give the same derivatives, in which case a specific activity of the material first injected would be assured.
* ↑ It has been pointed out in original communications that, in the parenteral introduction of carbohvdrates, no such regular results can be obtained as is the case with proteins: for the latter remain longer in the circulation, and are not usually excreted by the kidneys, The organism is, in this case, directly dependent on the composition of the products for its freedom from disharmonious substances. In the case of cane sugar, the kidneys are able of themselves to deal with the disharmoninus compound.
* ↑ Enteral sensitization and subsequent enteral shock have been successfully accomplished by us on two occasions only.
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