ANIMAL HEAT. 263 



A similar relation is manifest in the animal kingdom. Birds and 

 mammalians, whose respiration is most active, have the highest temper- 

 ature ; while in reptiles and fish, where the respiration is sluggish, the 

 production of heat is also less abundant, The connection between the 

 two phenomena is especially observable in hibernating animals, in 

 which, during the winter sleep, respiration becomes comparatively inac- 

 tive, and the bodily temperature is reduced to a very low standard. 

 In the observations of Horvath * on marmots, he found that these 

 animals during cold weather are plunged in a profound stupor, in which 

 their respiration is very infrequent and sometimes hardly perceptible. 

 At certain intervals they awake for a short time, and again return to 

 the state of insensibility. The internal temperature of the animal, when 

 awake, was from 35 to 37 C. ; while, in the hibernating condition, it 

 was reduced to 10, 9, or even to 2, according to that of the sur- 

 rounding air. On awaking, the temperature rapidly rises. In one 

 animal, during sleep, it was from 9 to 10 ; but on awaking it rose 

 in one hour to 12, in two hours to 17, and in two hours and a half 

 to 32. Respiration varies 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 hibernation. 



These facts indicate so close a relation between the intensity of res- 

 piration and that of heat production, that either one of these processes 

 may be taken, in general terms, as the measure of the other; particu- 

 larly as respiration consists in the absorption of oxygen and the exhala- 

 tion of carbonic acid, and as the oxidation of carbonaceous matters, 

 outside the body, is one of our readiest means for the production of 

 heat. 



But respiration is not exclusively connected with heat-production. 

 It is essential to all the manifestations of animal life, and may be taken 

 as the criterion of vital activity in general ; and a further study of 

 its phenomena shows that the heat of the living body cannot be con- 

 sidered as due to direct oxidation. 



The Evolution of Heat and the Products of Respiration not strictly 

 proportional. Notwithstanding the general relation in activity 

 between respiration and heat-production, a comparison of the quan- 

 tity of heat produced, and that of oxygen absorbed or of carbonic 

 acid exhaled, under different circumstances, shows that they do not 

 exactly correspond with each other. In the observations of Senator 

 on dogs, the evolution of heat and the production of carbonic acid did 

 not follow the same rate of increase. They were both augmented 

 during digestion, but the production of carbonic acid never increased 

 to the same degree with that of heat. The averages obtained in three 

 series of observations gave the following result : 



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



