412 NUTRITION. 



The relations of animal heat to the general process of 

 nutrition are most intimate. Any condition that increases 

 the activity of nutrition and of disassimilation, or even any 

 thing that increases disassimilation alone, will increase the 

 production of heat. The reverse of this proposition is equally 

 true. In pathology, the heat of the body may be increased 

 by a deficient action of the skin in keeping down the tem- 

 perature, without any increase in the activity of calorification. 



Influence of 'Exercise, etc., upon the Heat of the Body. 

 The influence of muscular activity upon animal heat is pecu- 

 liarly interesting in connection with the theories of calorifi- 

 cation, from the fact that the muscular system constitutes the 

 greatest part of the organism ; and, as has repeatedly been 

 shown by experiment, a muscle taken from a living animal 

 is not only capable of contraction upon the application of a 

 stimulus, but will perform for a time certain of the acts of 

 nutrition and disassimilation, such as the appropriation of 

 oxygen and the generation and exhalation of carbonic acid. 



The most complete repose of the muscular system is ob- 

 served during sleep, when hardly any of the muscles are 

 brought into action, except those concerned in tranquil respi- 

 ration. There is always a notable diminution in the general 

 temperature at this time. John Hunter found a difference, 

 in man, of about one degree and a half. 1 This fact has been 

 confirmed by all who have studied the question experimen- 

 tally. In the diurnal variations in the temperature of the 

 body, the minimum is always during the night ; and, as we 

 have already seen, this is not entirely dependent upon sleep, 

 for a depression in temperature is constantly observed at that 

 time, even when sleep is avoided. 8 



It is a matter of common observation, that one of the 



jusqu'ici de la respiration sur la temperature du corps humain. Archives de 

 physiologic, Paris, 1868, tome i., p. 496. 



1 HUNTER, Observations on certain Parts of the Animal (Economy, London, 

 1792, p. 114. 



2 See p. 407. 



