MODE OF PRODUCTION OF ANIMAL HEAT. 305 



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

 sumption or change of combination of its ingredients, it is evident that 

 in continued abstinence from food, the materials susceptible of this 

 change must be constantly diminishing in quantity ; and the animal 

 temperature accordingly, like other vital phenomena, becomes depressed 

 from a deficiency in the sources of its supply. 



Mode of Production of Animal Heat. 



In all instances, so far as observation has gone, the production of 

 heat in living organisms is in proportion to the activity of the internal 

 changes going on in the body. These changes are more especially and 

 constantly indicated by the absorption of oxygen and the exhalation 

 of carbonic acid in respiration. Even in the vegetable kingdom, it is 

 demonstrated by the researches of physiological botanists that the ab- 

 sorption of oxygen in plants is always accompanied both by the pro- 

 duction of carbonic acid and by the evolution of heat ; and the quantity 

 of heat produced is greatest at the time when those processes are going 

 on which, like germination and flowering, are accompanied by the most 

 active absorption and exhalation of oxygen and carbonic acid respec- 

 tively. 



The same thing is manifest in the different classes of the animal king- 

 dom. Birds and mammalians, where respiration is most active, have 

 also the highest temperature; while in reptiles and fish the respiratory 

 process is more sluggish, and the production of heat at the same time 

 less abundant. A very close connection between the two phenomena is 

 observable in hibernating animals, in which, during the winter sleep, 

 respiration becomes comparatively inactive and the bodily temperature 

 is also reduced to a very low standard. In the observations of Horvath 1 

 on the respiration of marmots, he found that these animals during cold 

 weather are plunged in a profound stupor in which the movements of 

 respiration are exceedingly infrequent and sometimes hardly perceptible. 

 At certain intervals the animals awake for a short time, after which 

 they again return to the state of insensibility. Horvath found that the 

 internal temperature of the marmot, when awake, was from 35 to 37; 

 while, in the hibernating condition, it was reduced to 10, 9, or even 

 to 2, according to that of the surrounding air. On awakening, the tem- 

 perature of the body rapidly rises. In one animal, the internal tempera- 

 ture during sleep was from 9 to 10 ; but on awakening it rose at the 

 end of an hour to 12, in two hours to 17, and in two hours and a half 

 to 32. Respiration also becomes increased in activity to a similar 

 degree. A marmot weighing 153 grammes produced, while in the 

 comatose condition, 0.015 gramme of carbonic acid per hour; and two 

 days afterward, when awake, produced 0.513 gramme in the same time, 

 that is, more than thirty times as much as when in the state of hiberna- 

 tion. 



1 Revue des Sciences Medicales. Paris, 1873, tome i. p. 59. 



