CHAP, xvi.] PHYSIOLOGICAL OFFICE OF RESPIRATION. 249 



On an average, respiration, or at least the primordial fact of 

 respiration consists, according to Regnault and Reiset, of an 

 absorption of oxygen, varying from 10 grammes to 0*09 in an 

 hour, and in a kilogramme of living matter. Besides, this 

 . oxygen transforms itself into carbonic acid and water in the 

 i proportion of 0*800 of a gramme combined with the carbon, 

 and of 0'200 of a gramme combined with the hydrogen. Finally, 

 there is an exhalation of azote representing about six-thousandths 

 of the weight of the oxygen consumed. These rough figures 

 must be accepted with great caution. Respiratory combustion 

 does not simply produce water and carbonic acid. These two 

 la.st bodies only result from the combustion of ternary substances ; 

 but quaternary substances oxydize themselves also, and their 

 oxydation gives birth to crystallizable, azotized elements, 

 eliminated by other outlets besides the pulmonary surface. 



However this may be, an important general fact results from 



the observations of Regnault and Reiset, corroborated besides by 



.1 those of many others ; namely, that the energy of the vital com- 



i bustion has a close connection with the nutritive and functional 



I movement. 



Thus, the quantities of oxygen absorbed, and of carbonic acid 



and azote exhaled, are about seven times greater amongst birds 



; than amongst mammif ers. In compensation, respiratory intensity, 



estimated after the same manner, is nearly ten times stronger in 



the mammifers than in reptiles (Regnault and Reiset). 



The respiration of insects, when these animals are in full 

 activity, has plainly the same energy as that of the mammifers, 

 whilst the earthworms do not respire more than reptiles ; but in 

 these comparisons the size of the animal must be taken into 

 account. In effect, the smaller the animal the larger the pro- 

 portion which the surface bears to its bulk ; consequently oxyda- 

 tion, which, as we shall see, is the principal source of animal 

 heat, must be more active since the coldness caused by peripheric 

 radiation is greater. 



Andral and Gavarret have made some very excellent observa- 



