262 FUNCTIONS OF NUTRITION. 



that in man there is a diurnal variation, the temperature during the 

 day being a little higher than at night, even when both periods are 

 passed in complete repose. A series of observations on the same indi- 

 vidual in a state of rest gave the following averages : 



TEMPEEATDEE or THE HUMAN BODY WHEN AT REST. 

 By day. By night. 



37.34 36.91 



The difference between the two averages amounts to 0.43. There 

 are also temporary variations of small extent during each of the above 

 periods ; the greatest variation during the day being 0.27 ; that during 

 the night 0.15. 



The temperature of the body is also increased by muscular activity. 

 It is a matter of common observation, both in man and animals, that 

 temporary exertion produces an increase of bodily warmth. Jurgensen 

 observed in the same individual that while during a day of absolute 

 rest, the maximum temperature attained was 31.7, under the influence 

 of exercise it reached 38.8. A much more striking difference, corre- 

 sponding with muscular repose or activity, has already been mentioned 

 as observable in insects. 



The animal temperature is furthermore increased or diminished by a 

 condition of digestion or abstinence. This was indicated in several 

 instances by the observations of Jiirgensen on man, but is shown in 

 a marked degree by those of Senator on the dog, in which the pro- 

 duction of heat was sensibly diminished by fasting, and increased by 

 food. The following table shows the heat produced by the same animal 

 under these two conditions : 



QUANTITY OF HEAT PEODUCED BY THE DOG IN ONE HOUE. 



After two days' fasting 10.90 heat units. 



After one day's fasting 12.63 " 



One hour after feeding 18.87 " 



As the production of animal heat can only take place by the con- 

 sumption or alteration of the bodily ingredients, it is evident that 

 during abstinence from food, the materials susceptible of this change 

 must diminish in quantity ; and the temperature of the body after a 

 time becomes lowered, owing to a deficiency in its sources of supply 



Mode of Production of Animal Heat. 



In all instances, so far as observation goes, the production of heat in 

 living organisms is in proportion to the activity of their internal changes. 

 These changes are especially indicated by the absorption of oxygen 

 and the exhalation of carbonic acid. Even in vegetables, it has been 

 demonstrated that the absorption of oxygen is always accompanied by 

 the exhalation of carbonic acid and the production of heat ; and the 

 quantity of heat produced is greatest during the processes of germina- 

 tion and flowering, which are accompanied by the most active absorp- 

 tion and exhalation of oxygen and carbonic acid respectively. 



