# Popular Science Monthly/Volume 41/July 1892/Physiology and the Prevention of Disease

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* PHYSIOLOGY AND THE PREVENTION OF DISEASE.
By Dr. J. M. RICE.
THAT disease is far more prevalent than our knowledge of prevention justifies can hardly be doubted. An inquiry into the cause of this evil, as well as into the manner in which it can be removed, is therefore, in my opinion, not inopportune.
With few exceptions, that which is done at present for the prevention of disease is limited to improving the sanitary conditions surrounding the individual, in consequence of which two very important factors are left out of consideration: Firstly, that many diseases are caused by unfavorable internal conditions, which for the most part can be traced to imperfect development and improper modes of living; and, secondly, that exposure to unfavorable external conditions is not necessarily followed by illness, for the reason that the body itself offers a certain amount of resistance to the same. Unless, therefore, our efforts be extended *to the prevention of diseases arising from internal causes as well as to increasing the power of resistance, they must to a considerable extent remain inefficient.
As the means employed for the purpose of improving the surrounding conditions are well known, it will be unnecessary to enter into detail here regarding them. The deleterious substances in the outer world are principally germs and other impurities of various kinds in the atmosphere and food. That diseases arising from such causes have considerably diminished during the past few decades, owing to the attention given to isolation, disinfection, antisepsis, sewerage, cleanliness, ventilation, etc., is unquestionable.
The remaining elements in prevention, namely, the regulation of the internal conditions and the increasing of the power of resistance, are so intimately connected that they are furthered by the same measures.
Although the conditions upon which the power of resistance depends are for the most part obscure, physicians agree that, other things being equal, an individual is strongly guarded against disease when he is in good health, and that resistance diminishes when the vitality becomes lowered. Now, in order, that there may be good health, normal functional activity of all the organs is essential. By endeavoring to secure good functional action, therefore, we do all possible for increasing resistance to disease caused by unfavorable external influences; but, in addition, we obviously aid in the prevention of functional derangements which, together with their consequences, constitute a large percentage of all diseases.
​But where shall we look for guidance if we desire to learn how normal functional activity can be attained? Naturally, to the science which treats of the bodily functions, physiology; and we shall see in a moment that by the application of physiological principles, not only will the organs be temporarily aided in the performance of their functions, but, if continued, good physical development, that condition upon which permanent health depends, will be secured. Therefore, physiology is, as well as bacteriology, to a certain extent a science of prevention, but, in our eagerness to catch and exterminate germs, it has been pushed far into the background, though so much nearer home to us than the latter.
That physical development is an important element in the maintenance of health becomes obvious when we consider that, other things being equal, an organ performs its functions in proportion to its strength; hence, if all the organs be well developed, all the functions will be thoroughly performed.
But good physical development is the result of adequate nourisl17nent of all parts of the body, and such nourishment depends upon the proper performance of all the functions. That this does not lead us into an absurdity becomes evident when we consider that imperfectly developed organs may with assistance perform their functions efficiently, and physiology points out how this aid can be given. In consequence of this help, therefore, the organs develop and perform their functions properly with ever less assistance, and the condition of perfect health is gradually approached.
Now, if we assist the organs during childhood when they are weak, not only will much be done to secure good health during this period, but the age of maturity will be reached with a welldeveloped body, and good health, therefore, to a considerable extent assured through life. It is true that, under ordinary circumstances, a smaller body can be nourished, with weaker organs; but if as early as the sixth year a child begins to labor from five to seven hours daily the conditions are entirely changed. During childhood a large quantity of nourishment is required for growth alone, and, if a good share of this be expended in labor, it is clear that, unless something be done to compensate for this unnatural state of affairs, when the period of growth is over the body will be imperfectly developed, with very little chance of recovering the lost ground. When this is the case, the individual will be liable to be afflicted with poor health ever afterward; how often it now occurs is but too well known.
As to the means for assisting the organs in their labor, none is so powerful as muscular exercise. This agent not only plays an important part in the general nutrition of the system, having a ​favorable effect upon all the functions which, take part in the changes through which the food must pass before being converted into tissue, namely, digestion, absorption, circulation, oxidation, and assimilation; but it likewise aids in preventing derangement of these functions—that is, a large number of diseases. The following résumé of the effects of exercise will show that its value has not been overestimated:
First. Muscular contraction exerts a pressure upon the veins and lymphatics, thus pushing forward and facilitating the flow of venous blood and lymph, to the heart. In this manner the excretion of the products of tissue waste is enhanced. These matters are washed out of the tissues by the blood and lymph, and after their return to the heart pass through the lungs, where the carbonic acid is given off, then through the general circulation, the remaining substances being eliminated by the skin and kidneys. When these matters, some of which are highly poisonous, collect in abnormal quantities in the system, they become more or less dangerous; even such mild symptoms as headache, drowsiness, and general lassitude in those who lead a sedentary life may probably, in many instances, be traced to their toxic effects. By muscular exercise, which hastens the elimination of these substances, therefore, many slight ailments, which, however, are sufficient to make labor burdensome and rob life of many of its pleasures, may be avoided.
Second. The circulation is controlled mainly by the action of the heart. When the activity of this organ is increased, therefore, the general circulation will be improved. Now, the heart is stimulated to action by the presence of blood in its cavities, and muscular exercise, by hastening the flow of venous blood, will be instrumental in sending more fluid through them in a given period of time, and consequently in stimulating the organ to increased activity. As many diseases, prominent among which are those of the abdominal and pelvic organs, are the consequences of congestion, and as good circulation does much for the prevention of such congestion, muscular exercise, by improving the general circulation both by increasing the activity of the heart and aiding in the venous return, will do much to prevent a large class of diseases.
Third. The respiratory center is increased in activity when the blood is more venous than usual—that is, when the amount of oxygen is diminished and the carbonic acid increased. Now, as an organ consumes more oxygen and gives off more carbonic acid when it is actively engaged in the performance of its functions, it follows that exercise exerts a stimulating effect upon respiration by making the blood more venous. When the activity of respiration increases, a larger quantity of oxygen enters the system; ​and it has been calculated that this extra supply more than compensates for that expended in exercise—a circumstance which is readily understood when we consider that during muscular action more blood passes through the lungs, thus coming in contact with more oxygen. An increased supply of oxygen enhances the oxygenation of the food, thus directly facilitating the development of energy; and, besides, oxygen being a heart stimulant, the circulation will again be favorably affected.
Fourth. Assimilation becomes furthered by muscular exercise, for the reason that more blood passes through an organ during its activity, and consequently the latter becomes enabled to absorb more nourishment and lay by a larger quantity of reserve force.
Fifth. The blood, becoming more rapidly freed of its nutrient material by increased rapidity of assimilation, will be more ready to absorb such matters from the digestive organs. Improved absorption leads to more perfect digestion, and consequently muscular exercise aids considerably in the prevention of digestive disturbances. Further, when the digestion is enhanced, more food is called for. Increased appetite, together with improved digestion, absorption, oxidation, and assimilation, naturally exerts a marked influence upon the general nutrition of the system; therefore, exercise is a powerful means to the prevention of so many diseases caused by malnutrition.
Sixth. Muscular exercise by its direct effect upon the muscular system is the means not only of developing an active as well as a strong and healthy body, but likewise of storing up a large quantity of reserve force.
But, in order that muscular exercise may result in good physical development, it must be carried on systematically for a long period, and especially, for reasons already given, during the years of childhood. The nature of the exercise plays by no means an unimportant part in its efficacy. In order that all parts of the muscular system may be brought into play, gymnastics and calisthenics are indispensable. These exercises, however, should be supplemented by outdoor sports, such as games, rowing, swimming, skating, and the like, for two reasons: Firstly, the latter contain an element of pleasure without which that exhilaration which makes exercise doubly valuable is apt to be wanting; and, secondly, the air inhaled at the time is purer than that in closed rooms, an advantage which can not be overestimated.
But how can good physical development be placed within reach of all children? Only in one way, namely, by the introduction of effective methods of physical exercise into schools, for the reason that during the greater part of childhood systematic work outside of these institutions is, in the vast majority of cases, entirely out of the question.
​In our search for means of preventing disease we have been led, as we see, beyond the province of medicine and into that of education. But the connection between these two fields, from our standpoint, extends much further, as we shall find. Though muscular exercise be carried to the point of perfection, and the surrounding conditions leave nothing to be desired, health is not assured; for, should the expenditure of energy be too great, there will still be marked interference with development. Hence, the expenditure as well as the development of energy must be considered.
Now, the energy is expended by the organs in the performance of their functions. Though ultimately derived from the food, its proximate source is, at least in great part, the tissues, which, by undergoing combustion, furnish the required energy; whether it be all derived in this way, or whether it be in part supplied immediately by the blood, is a matter which has no influence upon our problem. It is essential, however, to bear in mind that the amount of energy which can be developed in a given space of time is limited to the quantity of food digestible during this period, and, if it be expended more rapidly than it is thus supplied, the functions are performed at the expense of the tissues. If, therefore, we desire to guard the system against waste and allow the organs to develop properly, we must, as far as possible, limit functional activity. There are, however, only two functions over which we can exert a direct voluntary influence, namely, the muscular and the mental. But as there is ample compensation for the energy expended in muscular activity while there is none, in the physical sense, for that used in mental action, it is clear that if we desire to economize we must do so by exercising control over mental labor. That the energy expended by the brain during its activity is derived from the same source as that required for the performance of the other functions is, to-day, a generally accepted fact.
But, in order that it may not interfere with physical development, mental labor must be regulated both quantitatively and qualitatively.
In regard to quantity, the number of school hours must not be excessive; and introduction into school life should be gradual, so that the labor may be in proportion to the age and strength of the child. In Germany this rule is observed, the children beginning with about sixteen hours per week, to which two are added every year until the fifth or sixth, when the maximum is reached. The amount of work required at school, and in the preparation of lessons, likewise needs careful consideration.
From the qualitative standpoint the methods of instruction play an important part. When the laws of psychology are observed, the mind being treated in accordance with its nature, the ​channels of least resistance are used, and the greatest amount of labor performed with a given amount of energy.
As long, therefore, as physical exercise is grossly neglected, and unpsychological methods of teaching remain in general use, disease must continue in abundance, though ever so many improvements be made in sewerage, ventilation, and disinfection; for, as our argument has shown, attempts at prevention will in great part remain ineffectual until good systems of physical and natural methods of mental development have been introduced into the schools.