Chap, xvi.] PHYSIOLOGICAL OFFICE OF EESPIEATION. 249 



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

 respiration consists, according to Eegnault and Heiset, 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 

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

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

 there fa 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 

 last bodies only result from the combustion of ternary substances ; 

 but quaternary substaoaces oxydize themselves also, and their 

 oxydation gives birth to crystallizable, azotized elements, 

 eliminated by other outlets besides the j)ulmonary surface. 



However this may be, an important general fact results from 

 the observations of Regnault and Reiset, corroborated besides by 

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

 bustion has a close connection with the nutritive and functional 

 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 reptUes ; 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- 



