514 NUTRITION. 



did he observe absorption of oxygen and exhalation of carbonic acid after the muscle had 

 been removed from the body of the animal, but he noted an elevation in tempera- 

 ture of about one degree Fahr., following contractions artificially excited. 



It is useless to multiply citations of experiments illustrating the facts above noted or 

 to discuss elaborately the theoretical transformation of a given quantity of caloric into 

 a definite and an invariable amount of work. The conditions in the animal economy are 

 siich that we cannot exactly appreciate the loss of heat by the cutaneous and respiratory 

 surfaces ; nor can we follow the processes in the body which involve the disappearance 

 of oxygen and the evolution of carbonic acid ; the exact changes undergone by the 

 hydro-carbonaceous elements of food and constituents of the body ; the amount of heat 

 involved in the changes of the nitrogenized elements ; and, in short, we cannot make 

 the corrections that are absolutely necessary before we can hope to reduce the question 

 of the oxidation of certain principles in the body, the development of heat, and the 

 generation of mechanical force, to exact mathematical calculation. 



Observations upon the influence of mental exertion on the temperature of the body 

 have not been so numerous, but they are, apparently, no less exact in their results. Dr. 

 Davy was the first to make any extended experiments upon this point and has noted a 

 slight but constant elevation during "excited and sustained attention." The same line 

 of observation has been followed by Prof. Lombard, who employed much more exact 

 methods of investigation. Prof. Lombard noted an elevation of temperature in the head 

 during mental exertion of various kinds, but it was slight, the highest rise not exceeding 

 the twentieth of a degree. It is stated, also, that the temperature of the body is increased 

 by the emotions of hope, joy, anger, and all exciting passions, while it is diminished 

 by fear, fright, and mental distress. Burdach, from whom the foregoing statement is 

 taken, cites an example of an elevation of temperature from 96 to 99 '5 in a violent 

 access of anger, and a descent to 92-75 under the influence of fear, but the- temperature 

 soon returned to 97*25. 



The nervous system exerts a most important influence over the animal temperature, 

 as it modifies the circulation and the nutritive processes in particular parts. The most 

 interesting of these influences are transmitted through the sympathetic system. These 

 will be discussed, to a certain extent, in connection with the theories of calorification ; 

 but they cannot be taken up fully until we come to consider the functions of the sympa- 

 thetic system and its relations to nutrition. In this connection, we shall simply allude 

 to certain phenomena manifested through the nervous system, without attempting to 

 fully explain their mechanism. 



It is well known that, when the sympathetic nerves going to a particular part are 

 divided, the arterial coats are paralyzed and dilated, the supply of blood is increased, 

 nutrition is locally exaggerated and more or less modified, and the temperature of the 

 part is increased by from five to ten degrees. An illustration of these facts in the ear 

 of the rabbit, after division of the sympathetic in the neck, is a very common observa- 

 tion, which we have often verified in public demonstrations. All of these unnatural 

 phenomena disappear upon galvanization of the divided extremity of the nerve. These 

 local modifications in the temperature have been frequently observed pathologically in 

 the human subject. A number of curious local variations of temperature can be explained 

 by direct or reflex action through the sympathetic nerves. 



It is evident that, if animal heat be one of the necessary attendant phenomena of 

 nutrition, it must be greatly influenced by conditions of the circulation. It has been a 

 question, indeed, whether the modifications in temperature produced by operating upon 

 the sympathetic system of nerves be not due entirely to changes in the supply of blood, 

 t is certain that whatever determines an increased supply of blood to any part raises 

 the temperature ; and, whenever the quantity of blood in any organ or part is consid- 

 erably diminished, the temperature is reduced. This fact is constantly illustrated in 

 operations for the deligation of large arteries. It is well known that, after tying a 



