# Defensive Ferments of the Animal Organism/Defensive Ferments of the Animal Organism/Section 2

​If we sum up all the phenomena observed, we get the following picture: By introducing substances which are out of harmony with the species, and more particularly with the plasma, we bring into the organism bodies which are, in their whole structure, absolutely disharmonious with the cells of the body. No alteration has as yet taken place. In order that these substances may be utilized by the cells of the body, the products that are suitable for the organism must be so far decomposed as to entirely lose their specific character. This decomposition is effected by ferments, and is certainly initiated very quickly, for the disharmony with the blood or plasma and the body may extend also to the cells, and have an injurious effect on them. During the decomposition of these substances products arise at first which are, in part at least, definitely disharmonious with the ​organism, and these may be equally injurious under certain conditions. If these products of a gradual decomposition constantly appear only in small quantities and further decomposition is very rapid, then the injury will be but trifling and transitory. When, on the contrary, a large quantity of these products of decomposition suddenly appear, they can produce serious disturbances by their combined action. In these processes it is not only their chemical nature, their structure and configuration, that is of importance; we have to remember that, during the decomposition of colloid substances, products arise which exert an influence upon the osmotic pressure, and may, in consequence, disturb the existing equilibrium. What we observe in the plasma also takes place, as we have already emphasized, in the interior of the cells, and probably in a similar way. It may be pointed out here that, when bodies of a simple constitution, such as crystalloids, are introduced, the organism is able to defend itself, not only by decomposing such disharmonious substances, but also by excreting a part of them, at any rate, through the kidneys. The same method of defence may be resorted to when, during the decomposition of complicated substances, simpler particles are produced. In this case the excretion accelerates the ejection of the disharmonious substance from the body. It is true that, in doing this, the organism loses valuable ​fuel on the one hand, and certain constructive units on the other.
Many observations point to the fact that parenterally introduced substances, in so far as they can be modified, are utilized by the organism; that is, they serve as nourishment. The digestion, which would otherwise take place in the intestine and prevent the passage of disharmonious material into the body, is performed by the blood.
It is an open question from what source these ferments, which we are going to call defensive ferments, take their origin. Many facts accord with the suggestion that the leucocytes play a part in this connection (see also Lit. 23). They probably give off these ferments to the circulation. If so, we should then have in the blood plasma phenomena more or less analogous to those observed, for instance, by B. Friedrich Müller, during the dissolution of the fibrin that is excreted into the alveoli in cases of pneumonia. We see here numerous leucocytes penetrating into the solid exudate and dissolving it, after which an absorption of the products of decomposition begins, a kind of digestion taking place in the interior of the alveoli. Here also, as can be shown by special experiments, ferments can be demonstrated in the contents of the alveoli (in the expectorated sputum) and these ferments take their origin from the leucocytes. The old view, whereby the leucocytes take up ​substances from the outside and digest them, must now be completed by the observation, that ferments can be given off to the exterior, and that therefore digestion may be accomplished outside the cell. We would like for the present to leave the question open, whether any importance can be ascribed, in this connection, to the white blood corpuscles generally, or to any special forms of these. We presume that the red blood corpuscles as well, and very likely also the blood platelets, play an important part in these processes. The presence of ferments in these cells must not, it is true, be unconditionally connected with the formation of defensive ferments, because it is clear that these cell elements must have means of reducing their nutriment to simpler molecules, and constructing their own bodies. In any case, it is extraordinary that, in these kinds of cells, there are such active ferments present, and in such large quantities. According to our experiments, the splitting processes in these cells take place much quicker than in the other cells of the body. It is certain that the red blood corpuscles have, besides the function of transporting the oxygen, other duties to fulfil in the economy of the organism. We further consider it quite possible that the same cells, which give off insufficiently harmonized products to the blood, also supply the ferments which are able to complete the decomposition in the circulation.
​According to our observations, there is not the slightest doubt that the animal organism is not left without means of defence against disharmonious substances. If such products make their way into the body, the latter sends out defensive ferments that are directed against special kinds of substrates. Not only do they effect the destruction of the specific character of the parenterally introduced substance by means of an extensive decomposition, but they render possible the utilization of the products of the decomposition in the general metabolism. The reaction we have demonstrated enables us at any time to decide whether a certain substance is in harmony with the body or not. We have already emphasized the fact that we must distinguish not only substances that are in, or out of, harmony with the body, but also those which are in, or out of, harmony with the blood or its plasma, or again with the cells. We have already described how the intestine, with its ferments and those of its accessory glands, decomposes all disharmonious substances until an indifferent mixture of only the simplest units is left; and how then the cells of the gut-walls, and of the liver, carefully test the absorbed products for the absence, or transformation, of all substances that are out of harmony with the body and blood. Moreover, all the cells of the body take care that nothing shall pass from them into the circulation which has not attained a certain ​grade of decomposition. For further protection, the lymph, with all its complicated arrangements, is interposed between the circulation and the cells of the body. Here everything is tested afresh; and nothing is let loose into the circulation that has not been rendered harmonious with the blood and its plasma. For ourselves, we have scarcely any doubt that the lymph system plays an important part in metabolism, along the lines we have indicated. Sometimes substances are reduced and converted into harmonious material; sometimes products of a definite type are built up. The lymph is, as we have pointed out before, to be considered as a sort of buffer between the cells of the blood and those of the body; as a neutral zone, in which everything is assimilated as far as possible.
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