194 The English School [lect. 



not necessary for the transit is shewn by the simple experience 

 that " when you hold your breath as long as you can the finger 

 " on the pulse will tell you that blood is still rapidly passing 

 " into the arteries," and therefore must have made the transit 

 through the quiescent lungs. 



Still another opinion that the blood is agitated, comminuted 

 and broken as it were into very minute particles, is also according 

 to him wrong, for any air would produce this mere mechanical 

 effect, and air vitiated by some contagion or air which had 

 been breathed over and over again would be equally good for 

 respiration. 



"And indeed if the need of breathing only arose as some 

 " have thought, in order that the mass of the blood should be 

 " thoroughly shaken by the movements of the lungs and broken 

 " up as it were into extremely minute parts, there would be no 

 " reason why an animal should so quickly expire when shut up 

 "in a flask in the manner stated. For the air in the flask 

 " even after the death of the animal is quite as well fitted as 

 "before for the inflation of the lungs and so for the comminu- 

 " tion of the blood. For since that air is still subject to the 

 " pressure of almost the whole atmosphere, there is nothing 

 " to prevent its being driven into the dilated thorax of the 

 " animal, it being this, as I have elsewhere said, on which the 

 "inflation of the lungs depends." 



No, he says, it is evident that something belonging to 

 the air, whatever it be, something necessary for sustaining 

 life passes from the air into the blood. Hence air which has 

 been already breathed and which has in consequence been 

 exhausted of those vital particles, is no longer fit for being 

 breathed again. 



" On the one hand it clearly appears that animals exhaust 

 " the air of certain vital particles which are of an elastic nature. 

 " On the other hand there cannot be the slightest doubt but 

 " that some constituent of the air absolutely necessary to life 

 "enters into the blood in the act of breathing. 



" We have no right to deny the entrance of air into the 

 "blood because on account of the bluntness of our senses we 

 " cannot actually see the vessels by which it makes its entrance. 



