during its circulation through the systemic capillaries, the caloric obtained from the atmosphere is transferred to the solids, by which their temperature and vitality are maintained, when the blood returns to the right side of the heart of a dark modena hue, having lost its power of stimulating the organs, until it acquires an additional quantity of caloric from the lungs. Dr. Prout observes, in his late Bridgewater Treatise, that "the phenomena of life are wholly removed from the logic of quantity." But if respiration be the source of animal life, the phenomena are resolvable into additions and subtractions of measurable elements; and it is only because they have not been ascertained with numerical accuracy, that physiology has never yet been reduced to the character of an exact science. For if it be true that the conversion of food into chyme and chyle is effected by its union with gastric juice, bile, and pancreatic liquor; that chyle is transformed into more highly organized particles of blood, by giving off water, carbon, and hydrogen, while passing through the lungs, in exchange for which it receives caloric from the atmosphere, with variable proportions of nitrogen, there is no good reason why the proportions of each should not be reduced to "the logic of quantity." According to some recent experiments of Dr. Ure, caloric enough is evolved during the combustion of 1 lb. of charcoal to melt 75 lbs. of ice, which would raise 150 lbs. of water 70°. Now if we suppose that 45,000 cubic inches of oxygen are consumed by a healthy man in 24 hours, making about 2 lbs. in round numbers; and that 40,000 cubic inches, or a little more than 1 lb. 12 oz. are expired in the form of carbonic acid, it must unite with about 12 oz. of carbon ;* so that if the same proportion of caloric be given out as in ordinary combustion, it ought to compensate the loss of 521° in a man weighing 150 lbs. And if the remaining 5000 cubic inches of oxygen combine with 4th its weight of hydrogen, (we have seen that the proportion of oxygen which disappears is generally much larger in carnivorous animals,) it ought to raise the temperature of 150 lbs. of water 12°; allowing, with Dr. Thomson, that caloric enough is evolved during the combustion of 1 lb. of hydrogen to melt 400 lbs. of ice. Lavoisier and Laplace inferred, from their experiments, that during the combustion of 1 lb. of charcoal, caloric enough was evolved to melt 96 lbs. of ice; and that nearly the same amount was given off by animals in proportion to the * Dr. Dalton calculated that the aliment which he took in 24 hours contained about 11 oz. of carbon; but that the mean quantity exhaled from the lungs did not exceed 10 oz.; the remainder passing off with the other excretions. He thinks that of the 6 lbs. of food and drink taken daily by a healthy man, 1 lb. consists of carbon and nitrogen, the remainder being chiefly water. (Manchester Memoirs, Vol. II. N. Series; and Ed. New Phil. Journal, 1832, 1833.) DULONG AND DESPRETZ. quantity of oxygen consumed by respiration. But on repeating their experiments, by surrounding animals with water, and comparing the elevation of its temperature with the amount of oxygen consumed, Dulong and Despretz inferred that from 9 to 25 per cent. more caloric was imparted to the water than could be accounted for by the absorption of oxygen, (in accordance with the theory of Lavoisier and Laplace,) allowing it to combine with carbon and hydrogen; and that in no case did respiration afford more thanths of the heat given off by the animal. M. Despretz, therefore, concludes that respiration is the principal source of animal temperature, but that a small remaining portion (petite portion restante) is generated by motion of the blood, friction, assimilation, &c. (Ann. de Chim. et de Phys. t. 26.) But it is scarcely possible to believe, that animals could remain from one hour and a half to two hours surrounded with water, without losing more caloric than they gain from the atmosphere by breathing, or that they should not undergo a reduction of temperature; and if it were established that they give out th more caloric, in proportion to the amount of oxygen consumed, than is evolved during the union of the same quantity of oxygen with carbon and hydrogen out of the body, I should still maintain that the process of combustion, by which animal life is supported, is perfect; whereas that of the 10 chemist is always more or less imperfect, and attended with loss from radiation, not to mention other sources of error. In My own opinion is, that instead of invalidating, the experiments of Dulong and Despretz are strongly in favour of the chemical theory proposed by Black, and supported by the most distinguished physiologists of modern times. regard to the hypothesis of M. Despretz, that "the small remaining portion" of caloric not accounted for by respiration, is generated by motion of the blood, friction, assimilation, &c. I answer, that whenever the process of respiration is arrested, the motion of the blood, friction, assimilation, &c. are no longer carried on, and that the temperature of the whole system falls rapidly to that of the surrounding medium. In reply to the arguments of Brodie, Philip, Tiedmann, Edwards, and others, who contend that animal heat is generated by nervous influence, secretion, nutrition, the condition of the blood, and muscular contraction, I shall proceed to prove that the mean healthy temperature of all animals is directly in proportion to the amount of their respiration; without which there could be no sanguification, secretion, nutrition, nervous influence, nor muscular contraction, and that they have mistaken effects for the cause of animal heat. CHAPTER III. Influence of Respiration on the Temperature and "If errors had not been rooted in men's first notions, some things justly discovered might have rectified others; but as errors have been fundamental, and of such a kind that men have rather neglected and passed things over, than formed a wrong or false judgment about them, it is no wonder if they never attained what they never had in view; not arrived at the end they never proposed; nor performed the course which they never entered." BACON. If ever the theory of Medicine be destined to take its appropriate rank among the exact sciences, it must be founded on precise and enlarged views of the cause which governs all the movements of nature, including those of the animal economy. And there is abundant reason to hope, that when the attention of mankind shall be once thoroughly aroused to the importance of throwing off the paralyzing trammels of authority, they will very soon be able to dispel the numerous obscurities that have hitherto retarded the progress of discovery. For it is certain that if the cause of sanguification, digestion, secretion, nutrition, sensation, and muscular motion be derived from the air by breathing, it must be a positive agent, subject to |