FUNCTIONS OF ANIMALS* 



oxygen which disappears above what can be accounted for by the 

 formation of carbonic acid gas to the formation of water. Then 

 from 0*69 to O80 of the whole heat evolved is produced by re- 

 spiration, and from 0*31 to 0*20 by other and unknown agencies. 

 I have myself little or no doubt that the whole animal heat 

 evolved is owing to the conversion of the oxygen gas absorbed 

 into carbonic acid and water during the circulation. In Des- 

 pretz's experiments the animals were exposed to a greater cool- 

 ing agency, from being surrounded by cold water, than in ordi- 

 nary respiration. If we admit that the great object of respiration 

 is the generation of heat, and adopt the statement made in this 

 chapter as accurate, there will be no difficulty in calculating the 

 average quantity of heat produced in man during twenty-four hours. 

 The blood in an adult is about 26 Ibs. avoirdupois, and it com- 

 pletes its circulation through the body in about 3*06 minutes. 

 Hence, 8^ Ibs. of blood pass through the lungs in a minute. 



During each inspiration, 16 cubic inches of air enter the lungs, 

 and 0*425 Ib. of blood is exposed to its action. During every 

 inspiration, 0-6432 cubic inch of oxygen gas is absorbed by the 

 blood ; and as every 4*75 cubic inches of oxygen gas, combin- 

 ing with carbon or hydrogen, evolved 1 of heat, it follows that 

 the oxygen absorbed during each inspiration evolves (during its 

 circulation in the blood-vessel) 0-17, or nearly one-sixth of a de- 

 gree of heat. The oxygen absorbed during 6 inspirations pro- 

 duces 1 of heat. Hence, the heat evolved by respiration in 

 twenty-four hours would heat 1 Ib. of water, 4800, or, suppos- 

 ing none of it dissipated, it would heat a middle-sized man 33 

 in twenty-four hours. 



Those who inhabit cold climates require more heat than those 

 who live in hot climates. Hence, doubtless, the reason of the 

 great appetites, and the vast quantity of whale oil swallowed by 

 the Esquimaux, and the small appetite and vegetable diet of the 

 inhabitants of the torrid zone. 



This subject has been placed in a very clear light by Liebig in 

 his late work on Animal Chemistry. Respiration, he conceives, 

 is intended to generate heat, without which no animal could live. 

 This is effected by the combination of the oxygen of the atmo- 

 sphere with the carbon and hydrogen of the food. He considers 

 the unoxygenized portion of food (starch, gum, and sugar) to be 

 intended for the production of animal heat But it is difficult 



