HUMAN PHYSIOLOGY. BOOK FIRST. STATICAL PHYSIOLOGY. CONDITIONS OF LIFE. CHAPTER I. Conditions of Life.-Nature and Sources of Substances supplied to the Body.-Annual Quantities required.—Table of Physiological Standards.—Animals do not create, but transform Substances.-Properties and Quantities of Matters received by the System.-Properties and Quantities of those it restores.-Heat of the Body arises from Combustion.-Cooling Agencies in an Animal.-Necessity of Repairs in the System.-Physical Aspect of Man.-The Soul.-The Vital Principle. Importance of Physical Science to Physiology. FOR the maintenance of the life of man three chemical conditions must be complied with. He must be furnished with air, water, and combusti ble matter. Under the same conditions, also, all animals exist. Even in those which seem to furnish us with instances of departure from this Three condigeneral rule, the exceptions are rather apparent than real. To tions of life. breathe, to drink, to eat, are the indispensable requisites of life. If there be among insects some which seem never to take water, or among fishes some which never taste solid food, these peculiarities disappear as soon as we understand them properly. Where a high development has been attained, as in man, experience assures us that the same inevitable result awaits a cessation of respiration for a few moments, an abstinence from water for a few hours, or from food for a few days. The supply of a part of these necessaries of life is adjusted to the urgency of the want. The act of breathing is incapable of de- Sources of suplay, but the air is accordingly every where present, and al- ply of material. fit for use. We can bear with thirst for a little time, and the earth here and there furnishes her springs and other stores of water. But far otherwise is it in the obtaining of food. It is the lot of all animals to secure nourishment by labor, and even of men the larger proportion, both ways in civilized and savage countries, submit to a hard destiny. To obtain their daily bread is the great object of life. What is the philosophical explanation of this necessity for a supply of air, of water, of food? Why is it that the system will bear so little delay ? The answer which Physiology gives to these questions is an answer of ominous import, but the whole science is a commentary on Life depends of material. The condition of life is death. No part of a living mechanism can act without wearing away, and for the continuance of its functions there is therefore an absolute necessity for repair. It has been greatly to the detriment of physiology and the practice of medicine that this conception has not been thoroughly realized until late times. The aspect of identity which an animal presents is an illusion, hiding from us the true state of the case. It has been the fruitful source of errors which have retarded the progress of these sciences. What could their career possibly be when men had persuaded themselves that a living being possesses a capacity for resisting any change, and that organic structures never yield to external physical influences until after death? But life, far from being a condition of immobility, is a condition of ceaseless change. An organism, no matter of what grade it may be, is only a temporary form, which myriads of particles, passing through a determinate career, give rise to. It is like the flame of a lamp, which presents for a long time the same aspect, being ceaselessly fed as it ceaselessly wastes away. But we never permit ourselves to be deceived by the simulated unchangeableness which such a natural appearance offers. We recognize it as only a form arising from the course which the disappearing particles take. And so it is even with man. He is fed with more than a ton weight of material in a year, and in the same time wastes more than a ton away. Conditions of man. There is, therefore, a general condition of equilibrium which every animal presents, depending upon its receipts and its wastes, a equilibrium in proper knowledge of the conditions of which is at the foundation of Physiology. That we may approach this problem under its simplest form, free it from all unnecessary complications, and make it of most interest to the special object of this book, the remarks now to be made will be confined to our own species, and, except when otherwise stated, to a condition of health, and to the adult period of life. To have a uniform standard of reference, we may assume one hundred and forty pounds as the weight of an adult healthy man. Now the constant consumption of food, water, and atmospheric air tends steadily to increase that weight, and even in a very short time a disturbance arising from these sources would be perceptible, were there not some causes of ANNUAL RECEIPTS AND WASTE IN MAN. 11 compensation. But even after a year, if a state of health is maintained, the weight may remain precisely what it was, and this may continue year after year in succession. in succession. The consumption of large quantities of solid, liquid, and gaseous matter does not therefore necessarily add to the weight. There are two periods of life for which this observation will not hold good. They are infancy and old age. During the former the weight increases from day to day, and during the latter it slowly declines. If there be thus causes for the increase of weight of the living system, there are also causes for its diminution. Setting aside the minor ones. these may be chiefly enumerated as loss by urine, by fæces, by transpired and expired matters. By transpired matters, are meant such as escape under the form of liquids and gases from the skin, and by expired matters, vapors and gases escaping from the lungs. There is, therefore, a tendency to an increase and a tendency to a diminution of the weight, and, in the condition of equilibrium we are considering, these must balance one another. If a man of the standard weight abstains from the taking of water and food, a good balance will prove that in the course of less than an hour he has become lighter. If he still persists, it needs no instrument to detect what is going on; the eye perceives it, for emaciation ensues. How, then, is it possible for a living being to continue at its standard, except the causes of increase are precisely equal in effect to the causes of diminution? Overlooking minor ones, we may therefore assert that the sum total of food, water, and atmospheric air taken in a given period of time is precisely equal to the sum total of all the losses by urine, fæces, transpired, and expired matters; for if the receipts were greater, the weight must increase-if the losses were greater, the weight must diminish. Persistency in this respect proves equality, and the case is just as simple as in the common affairs of life; he who pays less than he receives grows rich; if his payments are more than his receipts, he becomes poor; but his condition is unchanged if his payments and receipts are equal. Infancy, old age, and manhood answer to these circumstances respectively. matter required by man in a year. From the army and navy diet scales of France and England, which of course are based upon the recognized necessities of large Quantity of numbers of men in active life, it is inferred that about 21 pounds avoirdupois of dry food per day are required for each individual; of this about three quarters are vegetable and the rest animal. At the close of an entire year the amount is upward of 800 pounds. Enumerating under the title of water all the various drinks-coffee, tea, alcohol, wine, &c.—its estimated quantity is about 1500 pounds per annum. That for oxygen may be taken at 800 pounds. 12 ANNUAL RECEIPTS AND WASTE IN MAN. With these figures before us, we are able to see how the case stands. The food, water, and air which a man receives amount in the aggregate to more than 3000 pounds a year; that is, to about a ton and a half, or to more than twenty times his weight. This enormous mass may well attract our attention to the expenditure of material which is required for supporting life. It reveals to us the fact that the old physiological doctrine, that a living being is not influenced by external agents, is altogether a fallacy. A living being is the result and representative of change on a prodigious scale. Quantity of The condition of equilibrium which has just been set forth, moreover, leads to the conclusion that the aggregate weight of urine, matter yielded fæces, transpired, and expired matter is the same for the same period of time. In round numbers, we may take it at a ton and a half. by man in a year. It can not be questioned that the materials which are rendered back to the external world, after having subserved the purpose of the animal and passed through its system, are compounds of those which were originally received as food, drink, and air, though they may have assumed in their course other, and perhaps, in our estimation, viler forms. Recognizing as indisputable the physical fact that not an atom can be created any more than it can be destroyed, we should expect to discover in the substances thus dismissed from the system every particle that had been taken in. What, then, is man? Is he not a form, as is the flame of a lamp, the temporary result and representative of myriads of atoms that are fast passing through states of change-a mechanism, the parts of which are unceasingly taken asunder and as unceasingly replaced? The appearance of corporeal identity he presents year after year is only an illusion. He begins to die the moment he begins to breathe. One particle after another is removed away, interstitial death occurring even in the inmost recesses of the body. the system of man. From these general considerations we infer that the essential condition Great extent of of life is waste of the body; and this not only of the body the changes in in the aggregate, but even of each of its particular parts. Whatever part it may be that is exercised is wearing away, and wherever there is activity there is death. And since parts that are dead are useless, or even injurious to the economy, the necessities simultaneously arise for their removal and for repair. Much of the complicated mechanism of animal structures is for the accomplishment of this double duty. For an organic being to live, its parts must die. The amount of activity it displays is measured by the amount of death, and in this regard every member of the animal series stands on the same level. Here, at FIXED STANDARDS OF PHYSIOLOGY. 13 the very outset of our science, we must dismiss the vulgar error that the physical conditions of existence vary in different tribes, and that man is not to be compared with lower forms. We must steadily keep in view the interconnection of all, a doctrine which is the guiding light of modern physiology, and which authorizes us to appeal to the structure and functions of one animal for an explanation of the structure and functions of another. The more steadily we keep before us this philosophical conception of the interconnection of all organic forms, the clearer will be our physiological views. There has never been created such a thing as an isolated living being. uses of fixed From the manner in which these general considerations of the mechanical and chemical equilibrium of the system of man have been Necessity and introduced, it will doubtless be seen that it is the first busi- physiological ness of the physiologist to disentangle the variable results standards. which that system presents, as far as may be possible, and offer them under a standard estimate; that at the basis of this science there should be a table setting forth with the utmost exactness all the quantities concerned in such a standard type. Thus, assuming the weight of an adult man at 140 pounds, as we have done, it should show the diurnal consumption of combustible matter or food, of water, of air-the diurnal loss by evaporation, by secretion, by respiration. In contrast with this it should also give the nocturnal. It should also represent the quantity of bile, of saliva, of pancreatic juice; the weight of each one of the various salts and organic bodies they contain, the diurnal and nocturnal production of heat, &c. For the purpose of the practice of medicine, a standard of 140 pounds will perhaps be found most convenient, but in a scientific point of view, and especially for comparative physiology, a standard of 1000.parts is best assumed. I now present an attempt at the construction of such tables, it being perhaps scarcely necessary to apologize for their extreme imperfection. Though offering the results at present received as most trustworthy, a very superficial examination will show how full they are of errors and contradictions. Perhaps it would not be too much to say that it will require the labor of many physicians, continued for centuries, to bring such tables to the truth. Yet the approach to precision in these hypothetical constants will in all times be a measure of the exactness of physiology, and it may be added, also, of the practice of medicine. The time is at hand when such a typical standard must be the starting-point for pathology, and no rational practice can exist without it. The passage of physiology, from a speculative to a positive science, is the signal for a revolution in the practice of medicine. Moreover, physiology should furnish formulas for the computation of variations in these tabular numbers under variable conditions; as, for in |