516 NUTRITION. 



exclusively concerned in the production of heat. In the early history of the oxidation- 

 theory of Lavoisier, it was thought by some that the inspired oxygen combined with 

 the hydro-carbons of the blood in the lungs, and that the heat of the body was gener- 

 ated almost exclusively in these organs; but this idea has long since been abandoned. 

 We have already fully considered the question of the loss or gain in the temperature of the 

 blood in its passage through the lungs, and we have seen that there is, to say the least, 

 no constant elevation showing a generation of heat in these organs, sufficient to warm 

 the blood, and through it the different parts of the body. If we find that the blood in 

 coming from the lungs has about the same temperature as when it entered these organs, 

 it must be admitted that there is a certain generation of heat to compensate the loss by 

 evaporation from the pulmonary surface. As far as we know, the heat that results from 

 the mere physical solution of oxygen in the blood is all that is produced in the lungs. There 

 is no sufficient evidence to show that the lungs are special organs of calorification ; and 

 any generation of heat that takes place here is due, probably, to purely physical phe- 

 nomena in the blood. 



It is only necessary to refer back to the pages treating of the variations in the tem- 

 perature of the blood in different parts, to show that heat is produced in the general sys- 

 tem and not in any particular organ or in the blood as it circulates. The experiments 

 of Matteucci, showing an elevation of temperature in a muscle excited to contraction 

 after it had been removed from the body, and the observations of Becquerel and Bre- 

 schet, showing increased development of heat by muscular contraction, are sufficient 

 evidence of the production of heat in the muscular system; and, inasmuch as the muscles 

 constitute by far the greatest part of the weight of the body, they are a most important 

 source of animal heat. 



It has been demonstrated, by the experiments of Bernard, that the blood becomes 

 notably warmer in passing through the abdominal viscera. This is particularly marked 

 in the liver, and it shows that the large and highly-organized viscera are also important 

 sources of caloric. 



As far as it is possible to determine by experimental demonstration, not only is there 

 no particular part or organ in the body endowed with the special function of calorifica- 

 tion, but every part in which the nutritive forces are in operation produces a certain 

 amount of heat ; and this is probably true of the blood-corpuscles and other anatomical 

 elements of this class. The production of heat in the body is general and is one of the 

 necessary consequences of the process of nutrition ; but, with nutrition, it is subject to 

 local variations, as is strikingly illustrated in the effects of operations upon the sympa- 

 thetic system of nerves and in the phenomena of inflammation. 



Relations of Animal Heat to Nutrition. Nutrition involves the appropriation of 

 matters taken into the body and the production and elimination of effete substances. In 

 its widest signification, this includes the consumption of oxygen and the elimination of 

 carbonic acid ; and, consequently, we may strictly regard respiration as a nutritive act. 

 All of the nutritive processes go on together, and they all involve, in most warm-blooded 

 animals at least, a nearly uniform temperature. During the first periods of embryonic 

 life, the heat derived from the mother is undoubtedly necessary to the development of 

 tissue by a change of substance, analogous to nutrition and even superior to it in activity. 

 During adult life, animal heat and the nutritive force are coexistent. It now becomes a 

 question to determine whether there be any class of nutritive principles specially con- 

 cerned in calorification, or any of the nutritive acts, that we have been able to study by 

 themselves, which are exclusively or specially directed to the maintenance of the temper- 

 ature of the body. These questions simply involve a review of considerations with regard 

 to the relations of various of the functions to the production of heat. 



The supply of the waste of tissue being effected by metamorphosis of alimentary matter 

 a process, the exact nature of which we have not been able to determine it has thus 



