450 NUTRITION ANIMAL HEAT AND FORCE. 



Arctic explorers is that the use of alcohol does not enable men to endure a 

 very low temperature for any considerable length of time. 



As a rule, when the respiratory activity is physiologically increased as it 

 is by exercise, bodily or mental, ingestion of food or diminished external 

 temperature the generation of heat in the body is correspondingly raised ; 

 and on the other hand, it is diminished by conditions which physiologically 

 decrease the absorption of oxygen and the exhalation of carbon dioxide. 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 pro- 

 duction of heat. The reverse of this proposition is equally true. 



Notwithstanding the fact that there is a certain correspondence between 

 the activity of the respiratory processes and the production of heat, this is 

 far from being absolute. It has been shown by Senator that digestion in- 

 creases heat-production rather more than it increases the exhalation of carbon 

 dioxide. Muscular exertion has been found to increase the quantity of oxy- 

 gen consumed in very much greater proportion than it increased the heat- 

 production (Him). Even adding to the heat produced, the work, reduced to 

 heat-units, the heat-production was about doubled, while the quantity of 

 oxygen consumed was increased about four and a half times. 



Influence of Exercise etc., upon the Heat of the Body. The most com- 

 plete repose of the muscular system is observed during sleep, when hardly 

 any of the muscles are brought into action, except those concerned in tran- 

 quil respiration. There is always a notable diminution in the general tem- 

 perature at this time. In the variations in the heat of the body, the mini- 

 mum is always during the night ; and this is not entirely dependent upon 

 sleep, for a depression in temperature is always observed at that time, even 

 when sleep is avoided. It is a matter of common observation, that one 

 of the most efficient means of resisting the depressing influence of cold is 

 to constantly exercise the muscles; and it is well known that after long 

 exposure to intense cold, the tendency to sleep, which becomes almost irre- 

 sistible, if yielded to, is followed by a very rapid loss of heat and almost cer- 

 tain death. Muscular exercise increases the production of heat; but the 

 variations in the actual temperature of the body in man, although distinct, 

 are seldom very considerable, for the reason that muscular exertion is gener- 

 ally attended with increased action of the skin, which keeps the heat of the 

 body within restricted limits. In very violent muscular exertion, as in fast 

 running, the increased production of heat may be so rapid that it can not 

 be entirely compensated by evaporation from the skin, and the temperature 

 may rise to 104 Fahr. (40 C.). In about an hour and a half the tempera- 

 ture falls to the normal standard (Billroth, quoted by Landois). 



The elevation in temperature that attends muscular action is produced 

 directly in the substance of the muscle (Becquerel and Breschet). Intro- 

 ducing a thermo-electric needle into the biceps of a man who used the arm 

 in sawing wood for five minutes, these physiologists noted an elevation of 

 temperature of nearly two degrees Fahr. (1 C.). The production of heat 



