426 NUTRITION. 



Relations of Calorification to Respiration. Respiration 

 is one of the nutritive processes that can be closely studied 

 by itself, as it involves the appropriation by the system of a 

 single principle (oxygen), and that simply in solution in the 

 blood. There can be no doubt that, of all the nutritive acts, 

 respiration is, far more than any other, intimately connected 

 with calorification. As far as the general process is con- 

 cerned, the production of heat is usually in direct ratio to 

 the consumption of oxygen and the exhalation of carbonic 

 acid. In the animal scale, wherever we have the largest 

 amount of heat produced, we observe the greatest respiratory 

 activity. In man, whatever increases the generation of heat 

 increases as well the consumption of oxygen and the elimina- 

 tion of carbonic acid. The production of heat in warm- 

 blooded animals is constant, and cannot be interrupted, even 

 for a few minutes. The same is true of respiration. The 

 tissues may waste for w r ant of nourishment, but the heat of 

 the body must be kept near a certain standard, which is almost 

 always much higher than the surrounding temperature ; and 

 there is no other nutritive act so constant and so immediately 

 necessary to existence as the appropriation of oxygen. It is 

 not surprising, then, that early in the history of the physi- 

 ology of nutrition, before we knew, even, the exact condition 

 and proportion of the gases in the blood, it should have, been 

 thought that animal heat was the result of slow combustion 

 of the hydro-carbons. 



The physiological history of respiration and of animal heat 

 dates from the same series of discoveries. In the latter part 

 of the last century, the great chemist, Lavoisier, discovered 

 the intimate nature of the respiratory process, and applied 

 the theory of the consumption of oxygen and the evolution 

 of carbonic acid to calorification. We have already followed 

 out the progress of this discovery in connection with respira- 

 tion ; 1 and like nearly all of the great advances in physiologi- 

 cal science, the distinctly-enunciated idea was foreshadowed 



1 See vol. i., Respiration, p. 409, et seq. 



