Quite different is the explanation of these phenomena given by Lavoisier and de la Place." As a result of their experiments on a guinea-pig they conclude:

Ainsi, l'on peut regarder la chaleur qui se dégage dans le changement de l'air pur en air fixe, par la respiration, comme la cause principale de la conservation de la chaleur animale, et si d'autres causes concourent à l'entretenir, leur effet est peu considérable.

La respiration est donc une combustion, à la vérité fort lente, mais d'ailleurs parfaitement semblable à celle du charbon; elle se fait dans l'intérieur des poumons, sans dégager de lumière sensible, parce que la matière du feu, devenue libre, est aussitôt absorbée par l'humidité de ces organes: la chaleur développée dans cette combustion se communique au sang qui traverse les poumons, et de-là se répand dans tout le système animale. Ainsi, l'air que nous respirons, sert à deux objets également nécessaires à notre conservation; il enlève au sang la base de l'air fixe, dont la surabondance seroit très-nuisible; et la chaleur que cette combinaison dépose dans les poumons, répare la perte continuelle de chaleur que nous éprouvons de la part de l'atmosphère et des corps environnans.

la conservation de la chaleur animale est dûe, au moins en grande partie, à la chaleur que produit la combinaison de l'air pur respiré par les animaux, avec la base de l'air fixe que le sang lui fournit.

While the researches of Crawford and of Lavoisier and de la Place showed that the animal body was capable of giving off heat and that muscular work increased the oxidative processes, the fact that external muscular work could be converted into heat was first brilliantly demonstrated by Count Rumford. This investigator made experiments in which the work of horses was employed to turn a steel cannon-borer pressed against the bottom of a hollow metal cylinder immersed in water. He calculated that the heat produced by friction in such an apparatus was equal to that continuously produced in the combustion of 9 wax candles, each three-fourths of an inch in diameter. At the end of about two hours the water actually boiled. He says:

As the machinery used in this experiment could easily be carried around by the force of one horse (though to render the work lighter two horses were actually employed in doing it) these computations show further how large a quantity of heat might be produced by proper mechanical contrivance merely by the strength of a horse, without either fire, light, combustion, or chemical decomposition; and in a case of necessity the heat thus produced might be used in cooking victuals. But no circumstances can be imagined in which this method of procuring heat would not be disadvantageous; for more heat might be obtained by using the fodder necessary for the support of a horse as fuel.

Beginning with the experiments of Lavoisier, a new impulse was added to the search for the source of animal heat. Lavoisier's personal belief that the lungs are the seat of combustion was contested by Lagrange, who argued that if the quantity of heat developed in the body in the course of a day was actually produced in the lungs it would necessitate such a high temperature as to cause destruction. The discovery that respiration also took place through the skin independent of the lungs further complicated the matter. The discussion thus started waged continuously until in 1837 Magnus concluded that the combustion did not take place exclusively in the lungs, but in the capillaries in general throughout the entire body-a conclusion that has been accepted from that time.

a Lavoisier and de la Place, Mémoire sur la chaleur. Mémoires de l'Académie Royale des Sciences, 1780, p. 405, el seq. Printed in Paris, 1784.

Rumford's Essays, London, 1798, 2, p. 488.

Lagrange cited by Hassenfratz. Ann. de Chim., 1791, 9, p. 266.

d Spallanzani, Mémoires sur la respiration, Geneva, 1803.

e Magnus, Ueber die ein Blute enthaltenen Gaze; Sauerstoff, Stickstoff und Kohlensaure, Poggendorff's Ann. der Phys. u. Chem., Leipsic, 1837, 40, p. 583; 1845, 66, p. 177.

The absence of definite proof in Lavoisier's experiments that animal heat was actually a process of combustion led to various explanations as to the cause of production of heat. Brodie," working with decapitated animals, concluded from his experiments that the brain controlled the production of heat, and that it was due to a nervous action rather than a chemical change. In this he was supported by Chossat, but Hale in 1813, Legallois in 1817," Wilson Philip in 1817," and Williams in 1835 found on the other hand that artificial respiration in decapitated animals was ample to maintain the bodytemperature. All of these experiments, however, dealt only with measurements of body-temperature and not actually with the production of heat.

The first important calorimetric research was that resulting from the offer of a prize by the Academy of Sciences in Paris for the best essay on the origin of animal heat. The prize was awarded to a memoir by Despretz published in 1824. The essay of his competitor for the prize, Dulong, was read before the Academy in 1822 but not published until 1841, after Dulong's death. Both investigators employed essentially the same form of apparatus, namely, water calorimeters, and experimented with small animals such as rabbits and cats. According to Despretz, the heat of combustion of carbon and hydrogen accounted for 74 to 90 per cent of the animal heat; according to Dulong from 69 to 80 per cent."

In 1842 appeared the first of two papers by J. R. Mayer, the second paper appearing three years later in pamphlet form. In these papers Mayer enunciated and elaborated the fundamental principle now known as the law of the conservation of energy.

While formerly physiologists have been occupied in studying the balance of matter, i. e., the intake and output of the body, stimulated by the active researches of Boussingault' and Barral," after the enunciation of the principle of the conservation of energy by Mayer, the great problem came to be one of the balance of energy.

As early as Mayer's time we find physiologists considering the question of static work, for Mayer says: "Die Leistung eines Mannes, der mit grosser Anstrengung ein Gewicht frei hält, oder Stundenlang unbeweglich gerade steht u. s. w. ist = Null; ein Gleiches, ja noch viel mehr, kann auch eine hölzerne Figur vollbringen."

In the light of the present tendency toward vitalism, some of Mayer's statements have unusual force, since he dismissed as entirely irrational the idea of the creation of a physical force by means of a vital force. At this time Liebig" advocated the existence of a vital force, and Mayer was particularly emphatic in his polemic against Liebig's theory.

0

The best statement of the hold that "vitalism" had on the earlier

a Brodie, Philosophical Transactions, 1812, 102, p. 378.

b Chossat, Ann. de Chim. et de Phys., 1820, ser. 2, 15, p. 37.

cHale, Experiments on the production of animal heat by respiration, Boston, 1813.

d Legallois, Ann. de Chim, et de Phys., Paris, 1817, 4, p. 21.

e Wilson Philip, An experimental inquiry into the laws of the vital functions, London, 1817.

Williams, Observations on the changes produced in the blood in the course of the circulation, London, 1835. Despretz, Ann. de Chim. et de Phys., 1824, 26, p. 337.

h Dulong, Ann. de Chim, et de Phys., 1841, 1, p. 440.

1 See Despretz's comparison of the two investigations, Ann. de Chim. et de Phys. 1841, 2, p. 319.

1 Mayer, Ann. der Chem. u. Pharm., 1842, 42, p. 233.

k Mayer, Die organische Bewegung in ihrem Zusammenhange mit dem Stoffwechsel, Heilbron, 1845.

Boussingault, Ann. de Chim. et de Phys., ser. 2, 1839, 71, p. 113. Also ibid, ser. 3, 1844, 11, p. 433.

m Barral, Ann. de Chim. et de Phys., 1849, 25. p. 129.

n Liebig, Die organische Chemie in ihrer Anwendung auf Physiologie und Pathologie, Braunschweig, 1842. o Mayer, loc. cit., p. 57, et seq.

physiologists is found in a paper by Helmholtz," who, independently of Mayer, announced the same fundamental principle of the conservation of energy. In this paper Helmholtz says:

The majority of the physiologists in the last century and in the beginning of this century were of the opinion that the processes in the living bodies were determined by one principal agent which they chose to call the "vital principle." The physical forces in the living body they supposed could be suspended or again set free at any moment by the influence of the vital principle, and that by this means this agent could produce changes in the interior of the body so that the health of the body could be thereby preserved or restored. The present generation, on the contrary, is hard at work to find out the real causes of the processes which go on in the living body. They do not suppose that there is any other difference between the chemical and the mechanical actions in the living body and out of it than can be explained by the more complicated circumstances and conditions under which these actions take place, and we have seen that the law of conservation of force legitimizes this supposition. This law, moreover, shows the way in which this fundamental question, which has excited so many theoretical speculations, can be really and completely solved by experiment.

Although the calorimetric experiments of Despretz and Dulong, especially after their interpretation by Liebig, aided greatly in verifying experimentally the law of the conservation of energy in the animal body, it was not until the classical experiments of Rubner in 1893 on dogs, in which the income and outgo were accurately measured, that the law of the conservation of energy in the animal body was demonstrated. Subsequently, Atwater and his associates, working with the respiration calorimeter at Wesleyan University, Middletown, Connecticut, amplified the results obtained by Rubner, and by means of complete balance experiments, demonstrated this uniformity in the income and outgo of energy in the human body, thus proving the law of the conservation of energy. Simultaneously Laulanié in Toulouse made a series of observations with animals in an animal calorimeter which also further substantiated this important deduction.

Shortly after the announcement of the law of the conservation of energy by Mayer, an English engineer, Joule, computed the mechanical efficiency of a horse by comparing the amount of work performed with the energy in the food eaten. The following paragraph is from a paper by Scoresby and Joule:

A horse, when its power is advantageously applied, is able to raise a weight of 24,000,000 pounds to the height of one foot per day. In the same time (24 hours) he will consume 12 pounds of hay and 12 pounds of corn. He is therefore able to raise 143 pounds by the consumption of one grain of the mixed food. From our own experiments on the combustion of a mixture of hay and corn in oxygen gas, we find that each grain of food, consisting of equal parts of undried hay and corn, is able to give 0°.682 to a pound of water, a quantity of heat equivalent to the raising of a weight of 557 pounds to the height of a foot. Whence it appears that one-quarter of the whole amount of vis viva generated by the combustion of food in the animal frame is capable of being applied in producing a useful mechanical effect, the remaining three-quarters being required in order to keep up the animal heat, etc. If these theoretic views be correct, they would lead to the interesting conclusion (which is the same as that announced by Matteucci from other considerations) that the animal frame, though destined to fulfill so many other ends, is, as an engine, more perfect in the economy of vis viva than the best of human contrivances.

As the problem of the mechanical efficiency of the body came more and more to the front, many estimates with regard to the mechanical output of a

a Helmholtz, Proc. of the Royal Institution, 1861, 3, p. 356.

b Rubner, Zeitschr. f. Biol., 1894, 30, p. 73.

c Scoresby and Joule, Philosophical Magazine, 1846, 28, p. 454.

man's body during a day of work appeared in the literature. These computations, which are all based upon mathematical considerations entirely dissociated from chemical transformations in the body, present an interesting array of opinions. They are given in abstract in table 2. More recent estimates are not included.

1 Rankine, Manual of applied mechanics, 2d ed.. Glasgow, 1860, p. 626.

2 Donders, Nederlandsch. Arch. v. Genees.-en Natuurkunde, 2, p. 210. Also, Journ. Anat. Physiol., 1867, 1, p. 168.

3 Cited by Donders, Nederlandsch. Arch. v. Genees.-en Natuurkunde, 1864; also, Dublin Quarterly Journal of Science, 1866, 41, p. 469.

4 Haughton, Principles of animal mechanics, London, 1873, pp. 51-62.

5 Weisbach, Lehrbuch d. Ingenieur u. Maschinenmechanik, 2 Theil, 2 Abth., 5 Aufl., 1883-87, p. 83. Cited by Vierordt, Anat. physiol. u. physik. Daten u. Tabellen, Jena, 1893, p. 293.

6 Vierordt, Anatomische, physiologische und physikalische Daten und Tabellen, Jena, 1893, p. 293.

7 Trautwein, Engineer's Pocket Book. Cited by Carpenter, in The effect of severe and prolonged muscular work and the mechanical work and efficiency of bicyclers, by Atwater, Sherman, and Carpenter, U. S. Dept. Agr., Off. Expt. Stas. Bul. No. 98, 1901.

8 Thurston, The animal as a prime mover, Ann. Rept. Smithsonian Institution, 1896, p. 297.

9 Mosso, La fatigue intellectuelle et physique, Paris, 1894.

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

Beginning with 1850, investigations on the relation between metabolism and muscular work formed a considerable part of the researches of many physiologists. As time passed, the technique was more carefully developed and accuracy increased, since each succeeding investigation improved or attempted to improve upon the earlier ones; rapid progress in this field of research was thus assured. The literature, however, has its greatest value as a record of progress rather than as a series of mathematically exact contributions to the development of the general problem; consequently it is unnecessary to enter into an exhaustive digest of each paper, especially as this has already been admirably done in a number of articles which have appeared in handbooks and encyclopædias. A brief statement of the researches and the methods employed will therefore suffice, but in the subsequent discussion of the results of this investigation, specific reference will frequently be made to such portions of the earlier papers as deal particularly with the points under consideration.

The simultaneous measurement of the products of respiration and the heat outgo in experiments on man was first attempted in 1857 by Hirn." The study of the mechanical equivalent of heat which was engaged in at this time by many scientists led this investigator to make an attempt to deduce the mechanical equivalent of heat from a comparison of the heat and work simultaneously produced by a man with the calorific equivalent of the amount of oxygen consumed. Although his experiments were wholly unsuccessful," they marked a step in the attempt to establish the law of the conservation of energy.

The first extensive investigation into the influence of muscular activity upon the carbon-dioxide production was that made by Edward Smith, who early recognized the difficulties of computing the carbon-dioxide output of any individual owing to the unknown factor of muscular exertion. Smith, employing a mask and an absorbent for carbon dioxide, together with a gas-meter, estimated the amount of carbon dioxide excreted per hour under various conditions of muscular activity with and without food.

While walking at the rate of 2 miles per hour during three-quarters of an hour, and carrying a spirometer weighing 7 pounds, the investigator expired 18.1 grains of carbon dioxide per minute and 25.83 grains per minute while walking at the rate of 3 miles per hour. These quantities represent 1.85 and 2.64 times that of rest in the sitting posture. From these experiments Smith computed the quantities of carbon dioxide expired in quietude, by the nonlaboring class, and by laboring individuals. In quietude the results were 26.193 ounces of carbon dioxide per day, this being equal to 7.144 ounces of carbon; with the non-laboring class, 31.824 ounces of carbon dioxide, equal to 8.68 ounces of carbon; and with the laboring class, 43 ounces of carbon dioxide, equal to 11.7 ounces of carbon, with a general average of 33.67 ounces of carbon dioxide and 9.18 ounces of carbon per day.

Hirn, Recherches sur l'équivalent mécanique de la chaleur, Paris, 1858. This paper, subsequently rediscussed by Hirn (La thermodynamique et le travail chez les êtres vivants, Paris, 1887), was severely criticized by Chauveau (Arch. d. Physiol. norm. et pathol., 1897, 9, p. 229).. See Weiss, Physiologie générale du travail musculaire et de chaleur animale, Paris, 1909, p. 140, for a criticism of Hirn's results.

• Smith, Philosophical Transactions, 1859, 149, p. 681.