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CHAPTER XXX. 



ON ANIMAL HEAT. DEVELOPMENT OF HEAT IN PLANTS. DEVELOP- 

 MENT OF HEAT IN ANIMALS. TEMPERATURE OF THE HUMAN 



BODY. INFLUENCE OF EXERCISE, SLEEP, AGE, CLIMATE AND 



SEASONS, FOOD AND DISEASE UPON THE DEVELOPMENT OF HEAT. 

 HYBERNATION. THEORY OF ANIMAL HEAT. INFLUENCE OF 



THE chemical changes which are continually taking place in 

 animals and, at least under some circumstances, in plants, are 

 accompanied with the development of a certain amount of heat. 

 The elevation of temperature may be so slight as to elude the 

 ordinary means of observation ; and although the sensible temper- 

 perature of the organised body is very slightly higher than that of 

 the medium in which it is placed, the quantity of heat set free in 

 a given time may be considerable. This development of heat 

 seems to result from the action of the oxygen upon the combustible 

 elements of the food, and in a less degree upon those of the tissues. 

 The chemical combination in which the largest amount of heat is 

 disengaged in the higher animals, and upon which their high 

 temperature seems to depend, is that of carbon and oxygen, re- 

 sulting in the production of carbonic acid. 



Whenever oxygen combines with carbon, hydrogen, phosphorus, 

 sulphur, etc., or with a metal, heat is developed in an amount 

 exactly proportioned to the quantity of substance consumed. The 

 sensible temperature produced varies, however, with the intensity 

 and rapidity of the chemical action. When the action is intense, 

 the temperature rises very rapidly, and may reach a very high 

 degree for a short time. If, on the other hand, the action is slow, 

 the temperature may be scarcely elevated above that of the sur- 

 rounding medium; but this slight elevation may continue for a 

 considerable time. The quantity of heat developed in the two cases, 

 however, is precisely the same. 



Development of Heat in Plants. Heat is developed by the seeds 

 of plants during germination ; and at the same time oxygen is 

 removed from the air, and carbonic acid evolved. Buds, flowers 

 and ripening fruits also evolve a certain quantity of heat. 



