176 The English School [lect. 



to the ground. It was seen that as the blood-stream swept 

 through the lungs from the right to the left side of the heart 

 a great change in the blood took place ; from being venous it 

 became arterial. But what the change exactly was, or how it 

 took place, and what the connection was between the change 

 in the blood and the movements of the lungs, and indeed what 

 was the exact purpose of the bellows-like heaving and falling 

 of the chest remained unsolved problems. 



Van Helmont as we have seen, if we may distinguish 

 between his fourth and his fifth fermentation, thought that the 

 blood in passing through the lungs sutfered a fermentation 

 by which it became lighter in colour and more volatile, a 

 fermentation different from and introductory to that by which 

 the vital spirits were engendered in the left ventricle, and 

 across the septum in the right ventricle also. But he is not 

 clear on this point, and in any case he seems to have attributed 

 nothing to any mingling of the blood in the veins with the air 

 in the lungs. 



When we come to Borelli we pass at once into a clear 

 understanding of the problem so far as the mechanical side of 

 it is concerned. He applied to the mechanics of breathing the 

 new knowledge which had been arrived at on the one hand of 

 muscular contraction, and on the other hand of the pressure 

 and elasticity of the atmosphere, and so at once reached the 

 truth that inspiration consists in the entrance of air by virtue 

 of the pressure of the atmosphere into the chest enlarged by 

 the muscular contraction of its walls, and expiration in the exit 

 of the air so entering, mainly at least by cessation of contraction. 

 Fabricius had, as we have seen, some sound views on this 

 matter, but Borelli went far beyond him. 



When he came to deal with the chemical aspects of 

 breathing Borelli rejected instantly and peremptorily the old 

 view that the movements of breathing were for the cooling 

 and ventilation of the innate fire of the heart, or for expelling 

 the vapours generated by such a fire. 



In discussing the subject in his book he lays down by the 

 help of formulas and figures certain propositions concerning the 

 laws of mixture of the minute particles of diverse fluids exposed 



