No. 7. 



Animal Heat. 



227 



a single premium for the best plough, is per- 

 fectly ridiculous; it is like trying a race- 

 horse, a roadster, and a cart-horse, together; 

 or pitting a Merino, a Leicester, or a South- 

 down sheep against each other. Each is 

 valuable for particular purposes, and we 

 know from considerable practice, and much 

 personal observation, that different soils — 

 for instance, from heavy clay through the 

 several gradations to shifting sand, and the 

 different state again of these soils — whether 

 in green sward or naked fallow, or to turn 

 in a stubble and green crop, at least six 

 kinds of ploughs are requisite to perform 

 their work properly. — American Agricultu- 

 rist. 



Animal Heat. 



The source of animal heat, its laws, and 

 the influence it exerts upon the functions of 

 the animal body, constitute a curious and 

 highly interesting subject. 



All living creatures, whose existence de- 

 pends upon the absorption of oxygen, pos- 

 sess within themselves a source of heat, 

 independent of surrounding objects. 



This general truth applies to all animals, 

 and extends to the seed of plants in the act 

 of germination, to flower-buds when devel- 

 oping, and fruits during their maturation. 



In the animal body, heat is produced only 

 in those parts to which arterial blood, and 

 with it the oxygen absorbed in respiration, 

 are conveyed. Hair, wool, and feathers re- 

 ceive no arterial blood, and therefore in 

 them no heat is developed. The combina- 

 tion of a combustible substance with oxygen 

 is, under all circumstances, the only source 

 of animal heat. In whatever way carbon 

 may combine with oxygen, the act of com- 

 bination is accompanied by the disengage- 

 ment of heat. It is indiftent whether this 

 combination takes place rapidly or slowly, 

 at a high or at a low temperature; the 

 amount of heat liberated is a constant quan- 

 tity. 



The carbon of the food being converted 

 into carbonic acid within the body, must 

 give out exactly as much heat as if it had 

 been directly burnt in oxygen gas or in com- 

 mon air; the only difference is, the produc- 

 tion of the heat is diffused over unequal 

 times. In oxygen gas the combustion of 

 carbon is rapid, and the heat intense; in 

 atmospheric air it burns slower and for a 

 longer time, the temperature being lower; 

 in the animal body the combination is still 

 more gradual, and the heat is lower in pro- 

 portion. 



It is obvious that the amount of heat libe- 

 rated must increase or diminish with the 



quantity of oxygen introduced in equal times 

 by respiration. Those animals, therefore, 

 which respire frequently, and consequently 

 consume much oxygen, possess a higher 

 temperature than others, which, with a body 

 of equal size to be heated, take into the 

 system less oxygen. The temperature of a 

 child (102°) is higher than that of an adult, 

 (99.5°.) That of birds (104° to 105.4°) ig 

 higher than that of quadrupeds (98.5° to 

 100.4°) or than that of fishes or amphibia, 

 whose proper temperature is from 2.7° to 

 3.6° higher than that of the medium in 

 which they live. All animals, strictly speak- 

 ing, are warm-blooded; but in those only 

 which possess lungs, is the temperature of 

 the body quite independent of the surround- 

 ing medium. 



The most trustworthy observations prove 

 that in all climates, in the temperate zones, 

 as well as at the equator or the poles, the 

 temperature of the body in man, and in what 

 are commonly called warm-blooded animals, 

 is invariably the same; yet how different 

 are the circumstances under which they 

 live ! ^ 



The animal body is a heated mass, which 

 bears the same relation to surrounding ob- 

 jects as any other heated mass. It receives 

 heat when the surrounding objects are hot- 

 ter, it loses heat when they arc colder than 

 itself 



We know that the rapidity of cooling in- 

 creases with the difference between the 

 temperature of the heated body and that of 

 the surrounding medium ; that is, the colder 

 the surrounding medium, the shorter the 

 time required for the cooling of the heated 

 body. 



How unequal, then, must be the loss of 

 heat in a man at Palermo, where the exter- 

 nal temperature is nearly equal to that of 

 the body, and in the polar regions, where 

 the external temperature is from 70 to 90 

 degrees lower ! 



Yet, notwithstanding this extremely un- 

 equal loss of heat, experience has shown 

 that the blood of the inhabitant of the arctic 

 circle has a temperature as high as that of 

 the native of the south, who lives in so dif- 

 ferent a medium. 



This fact, when its true significance is 

 perceived, proves that the heat given off" to 

 the surrounding medium, is restored within 

 the body with great rapidity. This com- 

 pensation must consequently take place 

 more rapidly in winter than in summer, at 

 the pole than at the equator. 



Now, in different climates the quantity of 

 oxygen introduced into the system by respi- 

 ration, as has been already shown, varies 

 according to the temperature of the exter- 



