2o6 Mayow 



probable that nitro-aerial spirit, mixed with the 

 saline-sulphureous particles of the blood, excites in it 

 the necessary fermentation. And yet it is not to be 

 supposed that this effervescence of the blood takes 

 place in the heart alone, but that it goes on first in 

 the pulmonary vessels and afterwards in the arteries 

 no less than in the heart. For I do not recognise 

 that ferment, I know not what, in the left ventricle 

 of the heart. For whence and by what vessels is 

 there so great an influx of it as would suffice for 

 heating so often every day the whole mass of the 

 blood? In the foetus the blood to a great extent 

 passes directly from the right ventricle of the heart 

 into the aorta, and yet this ought not to be done if so 

 necessary a fermenta^tion took place in the left 

 ventricle. Much less probable is it that the beating 

 of the heart is caused by the rarefaction of the blood 

 in its ventricles as the famous Descartes supposed. 

 For if the pulsation of the heart were caused by the 

 fermentation of the blood in its cavities, then, when 

 the heart beat, its ventricles would be greatly dilated 

 by that blood, just as a bladder is blown into the form 

 of greatest capacity. And indeed the blood would 

 not rush forth so impetuously in the systole as in the 

 diastole of the heart, and not from an impulse derived 

 from the contraction of the heart, but on account of 

 its own rarefaction. But we know in fact, from 

 vivisections, that the ventricles of the heart are con- 

 tracted when it beats and are not dilated by the 

 rarefaction or explosion of the blood, and also that the 

 blood rushes out when the heart contracts but not 

 when it relaxes. Indeed, if a motion similar to that 

 which takes place in systole is excited in the heart of 

 a dead animal, filled with water or any liquid, the 

 liquid contained in it will immediately rush forth, not 



