122 RESPIRATION. L,ECT. VI. 



out much suffering, though their heads and branchiaB were 

 out of water, and their bodies alone immersed. Spallanzani 

 and Edwards have farther proved, that cutaneous respiration 

 is indispensable in the batrachians ; so that frogs can live 

 several days without lungs, but on the other hand, they 

 perish in a few hours if they are flayed or have their skin 

 varnished. A snake whose whole body is varnished soon 

 dies. Sorg immersed one of his arms in oxygen for four 

 hours ; at the expiration of this time he found that about 

 two-thirds of the gas had disappeared. Davy analyzed the 

 air which had been injected into the pleura of a dog, and 

 found that after a short time it yielded only slight traces of 

 oxygen. 



The mechanism of respiration, and the chemical changes 

 which accompany this function, take place, therefore, in all 

 animals in the same manner. Oxygen disappears in the 

 respiratory organs, and, at the same time, carbonic acid is 

 exhaled from them: there is more azote in the expired air 

 than in the air which was inspired ; the volume of the 

 carbonic acid evolved is never greater than that of the oxy- 

 gen absorbed ; and in certain animals it is one half less than 

 the latter, and the returned air is saturated with aqueous 

 vapour. 



Effects of Respiration. Whilst the respiratory act is 

 effecting the changes in the atmospheric air, which I have 

 now described, what happens in the organism? None of 

 you can be ignorant of the fact that, during respiration, the 

 venous blood, being carried to the lungs, loses its black- 

 ness and acquires a bright vermilion colour, becomes arte- 

 rial, is returned to the heart, and from this organ is sent to 

 all parts of the body. The interruption of this transforma- 

 tion occasions speedy death. 



I could adduce a great number of experiments to prove, 

 that the change of the venous into arterial blood takes place 



