A study of the mechanical efficiency of a steam-engine, an internalcombustion engine, or an electric motor is relatively simple, since conditions can be arbitrarily controlled and the output measured most accurately. On the other hand, with a mechanism as complicated as that of the human body, the exact measurement of the output of muscular work is very difficult and not readily controlled. Consequently, studies on the efficiency of the human body as a machine are impracticable in most physiological laboratories. Furthermore, the measurement of the income and the actual fuel consumption is greatly complicated by the fact that the human body can draw upon a reserve of its own material, while the supply of potential energy for the steam-engine, the internal-combustion engine, or the electric motor is determined solely by the actual amount delivered to it either through the steampipe, the gasoline or gas pipe, or electrical wires. But if it were possible to study the body-changes induced by a long course of training, to determine what changes take place, and why the body is more capable of extreme muscular activity, it would be logical and possible to lead up to a most rational method for producing this end and to explain the diversity in the training systems; the best features of the different systems could then be combined.

The results of such studies would have a practical value not only for athletes, but for those who are accomplishing large amounts of work. It is of vital importance to the contractor, to the railroad constructor, and to other large employers of labor, that their human machinery as well as their mechanical appliances work to the highest degree of perfection. They spend large sums of money in designing, repairing, and altering the most complicated machinery, but until recently no attempt has been made to increase the efficiency of the large number of workmen that they must necessarily employ. With the advent of scientific management," we see the dawn of a new era in muscular work and its relationship to large manufacturing and construction enterprises. Scientific management will, however, always fail in its purpose unless it is based upon a scientific foundation, and as yet there is a great paucity of physiological data on which to base such management of the human machine. That any one, or two, or a dozen series of investigations will completely revolutionize the methods of training, the dietary habits, or the hygienic conditions of a group of workmen is hardly to be expected. On the other hand, a carefully worked-out series of experiments for studying the mechanical efficiency of the human body, the relationship between muscular work and the total energy intake and output, the character of metabolism in the body as affected by muscular work, the problem of training as affecting the body-composition, and the relative readiness with which the different stores of material in the body can be drawn upon for fuel, will, if properly made, furnish fundamental data that ultimately should prove of the greatest value in a scientific adjustment of diet, hygienic conditions, and the application of the muscular work of man to levers and other mechanical appliances.

It is the purpose of this book to report a series of experiments conducted throughout the academic year of 1911-12 in the Nutrition Laboratory of the Carnegie Institution of Washington, located in Boston, with a professional athlete as subject. In these experiments the mechanical output was most exactly measured, and the chemical transformations inside the body were a F. W. Taylor, The principles of scientific management, New York, 1911.

studied with great accuracy. The relations between the character and the amount of material burned in the body, the total amount of muscular work, and the efficiency of the human body as a machine are all of peculiar and special interest, and considerable emphasis will be laid upon them.

PIONEER INVESTIGATIONS ON METABOLISM IN ITS RELATION TO MUSCULAR WORK AND ANIMAL HEAT.

GASEOUS EXCHANGE DURING MUSCULAR WORK.

It is outside the province of this report to enter into a detailed presentation of the experimental evidence which finally led to a knowledge of the source, the cause, and the mechanical equivalent of animal heat, and the development of the law of conservation of energy as applied to the human organism. For the proper understanding of the problems subsequently treated in this report, however, it is necessary to outline certain of the fundamental researches, especially those bearing upon the relationships between the gaseous exchange, the output of mechanical work, and the mechanical efficiency of the human body.

Prior to the time of Lavoisier, the conceptions of the physical and physiological processes as related to the chemistry of the human body were so devoid of scientific foundation that they can have now but little value except as an historic record of the trend of scientific thought at that time. With the advent of Lavoisier and his contemporaries, physiological and chemical research began to take a definite form which gradually led to the unfolding of natural laws and to the explanation of the phenomena of muscular action and of the transformations in the human body and their intimate relationships.

Lavoisier's activity in studying respiration resulted in two remarkable memoirs by himself and Séguin, the first of which was published in 1789." The results reported in this first memoir have particular significance in connection with the object of this book, in that Lavoisier recognized clearly the relationship between muscular activity and the gaseous metabolism, and not content with the simple determination of the carbon-dioxide excretion, actually attempted the determination of the amount of oxygen consumed.

The apparatus used in this research has been imperfectly described by Séguin, but his description tallies reasonably well with the two drawings attributed to Madame Lavoisier. A careful study of these drawings shows us, in the most illuminating way, the attitude of Lavoisier and his contemporaries towards respiration experiments. One of the drawings illustrates an experiment in progress with the man resting, and the other the conditions obtaining in an experiment made during muscular work. Evidently a mask was used, which Séguin states was constructed of copper and held in place about the neck by wax or cement. Of particular significance is the fact that in both drawings we see, as evidently an essential part of the experiment, a physician

Séguin and Lavoisier, Mémoires de l'Académie des Sciences, 1789, p. 566. Printed in Paris, 1793. Two excellent drawings of Lavoisier's laboratory, both showing studies in the respiration of men, are given by Grimaux (Lavoisier, 1743-94, Paris, 1899, facing pages 119 and 129 respectively). Tigerstedt has reproduced one of these engravings showing the conduct of an experiment during rest (Tigerstedt's Handbuch der physiologischen Methodik, Leipsic, 1911, 1, p. 72).

taking the pulse-rate of the subject. At the present day, when the relationship between the pulse-rate and metabolism is continually being emphasized, it is interesting to note that 130 years ago the importance of this relationship was also recognized by Lavoisier. In the experiments on muscular work a pedal arrangement, which is shown beneath one of the tables and to which the right foot of the subject is attached, was evidently used for performing the work. The amount of work was probably computed from the movements of the pedal. Of further significance is the fact that Lavoisier and Séguin recognized in their experiments that the subjects should be without food in the morning, a prerequisite of all modern respiration experiments. We can do no better than sum up the results in their own words:

Il résulte des expériences auxquelles M. Séguin s'est soumis, qu'un homme à jeun, dans un état de repos et dans une température de 26° de thermomètre de mercure, divisé en 80 parties, consomme par heure 1210 pouces cubes (24.002 litres a) d'air vital; que cette consommation augmenté par le froid, et que le même homme, également à ieun et en repos, mais dans une température de 12° seulement, consommé par heure 1344 pouces (26.660 litres) d'air vital.

Pendant la digestion, cette consommation s'élèvé à 1800 ou 1900 pouces (37.689 litres). Le mouvement et l'exercice augmentent considérablement toutes ces proportions. M. Séguin étant à jeun et ayant élève pendant un quart d'heure un poids de 15 livres (7.343 kilograms) à une hauteur de 613 pieds (199.776 mètres "), sa consommation d'air pendant ce temps a été de 800 pouces, c'est-à-dire de 3200 pouces (63.477 litres) par heure.

Enfin, le même exercice fait pendant la digestion a porté à 4600 pouces (91.248 litres) par heure la quantité d'air vital consommé. Les efforts que M. Séguin avoit faits dans cet intervalle oquivaléient a l'élévation d'un poids de 15 livres (7.343 kilograms) à une hauteur de 650 pieds (211.146 mètres) pendant un quart d'heure.

As a definitely planned series of experiments to study the influence of muscular work on the gaseous metabolism, this investigation is without precedent. That the results obtained are not in accord with those obtained by the use of the modern experimental technique can not dim in any way the brilliancy of the conception of the research.

Aside from these researches of Lavoisier and Séguin, the experimental evidence secured by the earlier investigators dealt almost exclusively with the gaseous excretion while the subject was at rest, the influence of muscular work being investigated but rarely. Owing to a limited technique, the determinations were as a rule confined to the percentages of carbon dioxide in the expired air. As an example of the wide variations found in the percentage of carbon dioxide in air expired in a supposedly normal manner, we may cite a collection of analyses gathered by Valentin." (See Table 1.)

C

Of the few researches regarding the influence of muscular work on the gaseous metabolism which followed those of Lavoisier and Séguin, that of Prout is the earliest. Prout, who used the method then in vogue of determining only the percentage of carbon dioxide in the expired air, states that he found the effects of exercise varied according to the nature and degree of the exercise and also according to its time and duration. Moderate exercise, as walking, seemed always at first to increase the percentage of carbon dioxide in the expired air, but after having been continued for some time, it ceased

a The reduction of pouces to liters, and of pounds and feet to kilograms and meters respectively, has been made by Gavarret (Physique médicale, Paris, 1855, p. 330).

b Valentin, Lehrbuch der Physiologie des Menschen, Braunschweig, 1847-51.

c Prout, Annals of Philosophy, 1813, 2, p. 328.

to produce this effect; if prolonged so as to induce fatigue, the quantity was diminished. On the contrary, violent exercise seemed to lessen the quantity, even from the first, or if it increased the amount of carbon dioxide excreted, the effect was very trifling. Following violent exercise, the percentage was always much less.

TABLE 1.-Percentages of carbon dioxide in expired air as cited by Valentin.

Since, as we now know, the percentage of carbon dioxide in the expired air is greatly influenced by the total ventilation of the lungs, it is obvious that these conclusions of Prout throw very little light upon the actual carbondioxide increment, although the fact that there was not a noticeable decrease in the carbon-dioxide percentage would of itself point to the fact that there must have been in all cases a considerably increased production—a fact that was many times unappreciated by the experimenters.

a

Later, Valentin and Vierordt showed, as did Prout, that movement increased the proportion of carbon dioxide contained in the gases expired. Vierordt was not able to make measurements of the carbon dioxide during work inasmuch as his method of testing required that the subject should be quiet; he emphasized the fact, however, that he could rely upon his pulse and respiration observations during the work, and upon the carbon-dioxide content of the air expired after the work for solving the problems of the effect of activity upon the metabolism. After a brisk walk he found a great increase in the carbon-dioxide excretion, corresponding to 80 c.c. of carbon dioxide per minute. His observations on the after-effect of work are also of interest. He shows that this is considerable, stating: "Es ist folglich die körperliche Bewegung von sehr grossem und nachhaltendem Einflusse auf die Ausscheidung der Kohlensäure."

Scharling also studied the influence of muscular work on the carbondioxide output, the work performed being the raising and lowering of a heavy iron bar. A marked increase in the carbon dioxide excreted was observed.

The influence of exercise on respiration was likewise studied by Lassaigne, who made some very interesting observations on horses. The first horse exhaled per hour before exercise 341.69 grams of carbon dioxide; after exercising 15 minutes, he exhaled 745.90 grams of carbon dioxide. The second horse exhaled per hour before exercise 658.38 grams of carbon dioxide; after exercise, the amount of carbon dioxide exhaled was 754.88 grams. He found, however, that exercise had no effect on the amount of carbon dioxide excreted

by a pure-blooded Arabian horse which, in the state of repose, exhaled 852.42 grams of carbon dioxide per hour. He states that the intensity of the respiration of this horse was remarkable. Lassaigne's technique was obviously faulty.

HEAT OUTPUT OF THE ANIMAL BODY.

The earliest attempts to measure the heat given off from the body of a living animal were those made simultaneously by Adair Crawford" in Glasgow and Lavoisier and de la Place in Paris. Crawford, with a water calorimeter, measured the heat given off from a guinea-pig and likewise made an estimation of the amount of carbon dioxide produced. Lavoisier and de la Place, using the melting of ice for the measure of the heat production, placed in their calorimeter a guinea-pig and weighed the water resulting from the melting of ice; subsequently they placed the guinea-pig under a bell-jar and determined the amount of carbon dioxide produced. Having tested their calorimeters by burning a wax candle or some pure carbon, both Lavoisier and de la Place on the one hand and Crawford on the other attempted to compute the amount of heat that would be required to produce the given amount of carbon dioxide. The results of their computations showed a fairly satisfactory agreement, indicating that the combustion was proportional to the amount of carbon dioxide produced. The interpretation of results is particularly interesting in showing that Crawford still adhered to the phlogiston theory, his explanation of the phenomena being determined chiefly by his experience with specific heats. According to his belief, the heat given off by the body is absolute heat which is abstracted from the pure air in its passage through the lungs, or, to quote him exactly:

That animal heat depends upon the separation of elementary fire from the air in the lungs is moreover supported by the experiments which have been brought in proof of the third and fourth propositions.c

In summing up his opinion, he says:

Hence it clearly follows, that, in the respiration of animals, as well as in the combustion of wax, oil, and tallow, the pure air is altered in its properties by its combination with the inflammable principle; and since we know that the union of these elements is universally accompanied with the extrication of heat, and particularly that, by this union, a large quantity of elementary fire is disengaged from the air in the combustion of oleaginous substances, we may conclude that, in the process of respiration, a similar extrication of fire takes place.d

Since, therefore, it has been proved that elementary fire is absorbed from the air in the process of respiration, and since the quantity that is thus absorbed is not only adequate to the effect which we have been endeavoring to explain, but also proportional to it, we may safely conclude that it is the true cause of animal heat.

Crawford distinctly states:

I do not mean to assert that elementary fire is really capable of being chemically combined with bodies. . . Before this can be admitted it must be proved that heat is a substance; and I do not know that any experiments have hitherto been published which demonstrate the materiality of that principle.

a Crawford, Experiments and observations on animal heat, 2d ed., 1788, J. Johnson, London. According to the preface of this book the experiments were made at Glasgow during the summer of 1777 and were presented to the Royal Medical Society during the winter of 1778. They were first published in 1779 (J. Murray, London, 1779).

Lavoisier and de la Place, Mémoires de l'Académie, 1780, p. 355. See also Lavoisier, Traité élémentaire de Chimie, Paris, 1801, p. 1. The irregularity incidental to the dating of publications issued between 1700 and 1880 has been the subject of comment by J. Rosenthal in a German translation of the two articles by Lavoisier and de la Place (Zwei Abhandlungen über die Warme von A. L. Lavoisier und P. S. de la Place, 1780 u. 1784. Ostwald's Klassiker der exakten Wissenschaften, No. 40, Leipsic, 1892). c Crawford, loc. cit., p. 358. e Ibid., p. 361. Ibid., p. 363.

d Ibid., p. 359.