Chap, xv.] EESPIRATOEY OEGANS IN ANIMAL KINGDOM. 229 . 



less rapidly when it is robbed of air ; and aerian abstinence is 

 always' supported for an infinitely shorter period than alimentary 

 abstinence ; always it is the more rapidly mortal, the richer the 

 nutrition. 



In the protozoa the exchange of gases is made by the whole 

 body. The oxygen impregnates the small protoplasmic mass, 

 transforms itself there into carbonic aeid, and comes out as it 

 went in by the simple action of osmosis. Moreover, the proto- 

 plasmic movement, especially where there are emission and 

 retraction of pseudopods, aids much the accomplishment of the , 

 phenomenon, by multiplying the contacts. This process, infinitely 

 simple, does not essentially diEEer from the processes with 

 complex diffierenciation so much as at fii-st sight might appear.. 

 Definitively, in superior organisms, every anatomical ■ element 

 holds the same relation- to the air which is observable in the 

 amorphous or monocellular protozoa. What constitutes the dif- 

 ference is the apparatus thanks to which the anatomical element 

 is brought into contact with the exterior atmosphere. 



Every organised substance not clothed with an impermeable 

 glaze, natural or artificial, respires more or less. 



Placing in closed vessels reptiles from which he had torn the 

 lungs, Spallanzani discovered that in these animals the skin acted 

 as a respiratory organ more vigorously than the lungs themselves. 



W. Edwards saw some frogs, whose lungs had been plucked 

 out, and whose neck was tightened by a ligature, live from twenty 

 to forty days when placed on humid sand in a chamber whose 

 temperature was +12 degrees. If, on the contrary, the frogs 

 were plunged in water when their teguments were no longer 

 in contact with the dissolved air, they perished in three 

 days. 



Humboldt and Provengal kept in vessels thoroughly separated 

 the body and the head of a tench, and they found that the body 

 absorbed oxygen, — in a word, respired. 



Even in mammifers in which exists a respiratory apparatus 

 voliuninous and with a vast surface, the skin plays an important 



