THE SOURCE OF MUSCULAR POWER. "It is now an established doctrine that force, like matter, can be neither created nor destroyed. The different forms of force are mutually convertible the one into the other, but they have their definite reciprocal equivalents, and in the transmutation the existing force undergoes no increase or decrease. The force liberated by a certain amount of chemical action will produce a certain amount of heat, and this, in its turn, may be made to accomplish a certain amount of mechanical work. The chemical action has its representative amount of heat, and the heat its representative amount of mechanical work; and the relative value of each is susceptible of being expressed in definite terms. It has been ascertained, for instance, that the force derived from chemical action which will raise the temperature of a pound of water 1° Fahr. will, under another mode of manifestation, lift 772 pounds one foot high; 772 foot-pounds are then said to constitute the dynamic equivalent of 1° of heat of Fahrenheit's scale. "What is true of force in the inorganic world is equally applicable in the organic. The force manifested by living beings has its source by transmutation from other forms which have preëxisted. The food of animals contains force in a latent state. Properly regarded, food must be looked upon, not simply as so much ponderable matter, but as matter holding locked-up force. By the play of changes occurring in the body the force becomes liberated, and is manifested as muscular action, nervous action, assimilative, secretory, or nutritive action, heat, etc." THE above is quoted from an article by Dr. F. W. Pavy, published in The Lancet for November 25, 1876. It contains a proposition which, if happily it were true, would mark an advance in our positive knowledge of animal mechanics, the importance of which could hardly be over-estimated— reducing our ideas of the physiology of muscular power to a degree of exactness and simplicity most attractive as well as desirable. I do not propose to discuss here the law of the correlation and conservation of forces, as developed by researches in physics and inorganic chemistry; but it seems to me that the unreserved and absolute application of this law to the mechanics of the living body, particularly in their relations to the source of muscular power, is a question for careful physiological investigation, and not one that can be accepted simply upon the basis of analogy. It is easy to follow the various chemical actions induced in inorganic matters, to measure the heat produced and calculate the corresponding equivalents of force; but, while we can observe these processes accurately and without serious difficulty, when we come to study the various changes and transmutations which organic matters undergo in the animal body, we meet with problems which are, perhaps, the most intricate and complicated in Nature. If the proposition advanced by Dr. Pavy were a legitimate and logical deduction from physiological investigations, nothing could be more simple than the mechanism of muscular power, and few would venture to contradict his views. This, however, does not seem to me to be the case. Dr. Pavy's proposition is apparently assumed to be true at the outset, as a condition precedent to his course of reasoning upon the results obtained by his observations. When the physiological data do not coincide with the theory under the influence of which his deductions seem to have been made, the error is assumed to be in the imperfection of the observations made by others as well as by himself. There is no suggestion that the theory itself may be faulty. Here seems to be the oft-repeated error of attempting to accommodate experimental facts to a law which is assumed to be invariable in its manifestations and exact in its applications; it is reasoning that a proposition, true as regards the inorganic kingdom, must be applicable absolutely to living bodies; it is bringing forward as evidence that the law is correct, arguments and deductions based mainly upon the assumption of the truth of the proposition involved. In the study of animal physiology, we constantly meet with phenomena which are analogous to nothing with which we are acquainted in the inorganic world; and processes, which at first seem to be simple enough in their explanation, have been afterward ascertained to be of the most complex character. A notable instance of the latter is to be found in the history of the connection between respiration and the 'production of animal heat. In 1775, Lavoisier, who is justly regarded as one of the greatest chemists that ever lived, ascertained that the gas obtained by decomposing the oxide of mercury "was better fitted to maintain the respiration of animals than ordinary air." Two years after, he confined animals under a bell-glass, and, after their death, showed that oxygen had been consumed and carbonic acid produced.' He afterward com 1 LAVOISIER, Mémoire sur la nature du principe qui se combine avec les métaux pendent leur calcination, et qui en augment le poids. Hist. de l'Acad. Roy. des Sciences, année 1775; Paris, 1778, pp. 521 and 525. • Expériences sur la respiration des animaux. Ibid., année 1777; Paris, 1780, p. 183. pared the changes which take place in the air in respiration with the changes produced by the combustion of carbon and advanced the theory that heat is produced by a process in the animal body analogous to combustion. "Respiration is merely a slow combustion of carbon and hydrogen, which is in every way similar to that which takes place in a lighted lamp or candle; and, from this point of view, animals which respire are true combustible bodies which burn and consume themselves." This was the origin of the theory which was afterward developed by Liebig into the doctrine of the hydrocarbons as calorific matters, and nitrogenized substances as plastic elements of food. While the theories of Lavoisier and of his followers very greatly advanced our knowledge of the respiratory processes, the more modern researches of Bernard, Brown-Séquard, and others, with regard to the influence of the nervous system upon calorification, local variations in animal temperature, etc., showed that the production of animal heat is one of the phenomena incident to the general process of nutrition and that it is not due simply to oxidation of hydrocarbons. Although oxygen is consumed, carbonic acid is produced, and heat is 1 SÉGUIN ET LAVOISIER, Premier mémoire sur la respiration des animaux. Hist. de l'Acad. Roy. des Sciences, année 1789; Paris, 1793, pp. 570 and 571. |