On Respiration 205 



ceases, yet the blood is transmitted through them to 

 the left ventricle of the heart. But if, on the other 

 hand, the mouth and nose be closed after breath is 

 taken and drawn into the lungs, death will certainly 

 follow, although the lungs remain inflated, because 

 expiration is prevented. And yet the passage of the 

 blood through the lungs is as ready in this case as in 

 the other ; for the comminution of the blood cannot 

 be greater in the former case, since in both cases the 

 lungs are equally distended — a clear proof that 

 respiration is not necessary either for the passage of 

 the blood through the lungs or for its agitation. But 

 the reason that an animal lives in the one case and 

 dies in the other is that in the former there is a 

 continual access of fresh air, but none in the latter. 



As to expiration, it should be noted that it serves 

 the further use that, along with the air driven out 

 from the lungs, the fumes which are raised by the 

 fermentation of the blood are also blown out. 



Let us now inquire what the aerial element is 

 which is so necessary to life that we cannot live for 

 even a moment without it. And indeed it is probable 

 that certain particles of a nitro-saline nature, and 

 these very subtle, agile, and in the highest degree 

 fermentative, are separated from the air by the action 

 of the lungs and conveyed into the mass of the blood. 

 For this aerial salt is so necessary to every form of 

 life that not even plants can grow in soil to which air 

 has not access. But if such soil be exposed to the air 

 and impregnated anew with this fertilising salt, it will 

 again become suitable for the nourishment of plants. 

 So that even plants themselves seem to have a kind 

 of respiration and the necessity of absorbing air. 



But it is not so easy to understand the function 

 which this aerial salt exercises in animal life, yet it is 



