512 NUTRITION. 



carbons of the blood in the lungs, and that the heat of the body was generated almost 

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



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 

 .system 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 Becquered and Bres- 

 chet, 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. 



Relation of Animal Heat to Nutrition. Nutrition and disassimilation involve the 

 appropriation of matters taken into the body and the production and discharge 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 prin- 

 ciples specially concerned 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 mainte- 

 nance of the normal temperature of the body. 



The supply of the waste of tissue being effected by a metamorphosis of nutritive mat- 

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

 thus far been possible, only, to divide the food into different classes. Of these, leaving 

 out oxygen and the inorganic salts, we shall consider, in this connection, the organic 

 matters, divided into nitrogenized and non-nitrogenized. 



What is the relation to calorification of those processes of nutrition which involve the 

 consumption of nitrogenized matter and the production of the nitrogenized excrementi- 

 tious principles ? 



We cannot study the phenomena of calorification alone, isolated from the other acts 

 of nutrition. We may confine an animal to a purely nitrogenized diet, and the heat of the 

 body will be maintained at the proper standard ; but at all times there is a certain quan- 

 tity of non-nitrogenized matter (sugar and perhaps fat) produced in the system, which is 

 formed only to be consumed. We may starve an animal, and the temperature will not fall 

 to any very great extent until a short time before death. Here we may suppose that the 

 process of deposition of nutritive matter in the tissues from the blood is inconsiderable, 

 as compared with the transformation of the substance of these tissues into effete matter ; 



