On Respiration 207 



indeed because of an explosion (for of course there is 

 no such thing in this case) but because the ventricles 

 actually contract. And further it is obvious that the 

 movement of the heart is not caused by the rarefaction 

 of the blood, because hearts are sometimes observed to 

 beat after being cut out even if the blood has been 

 pressed out of their ventricles. Indeed, if a solution 

 of opium or cold water be injected through the 

 jugular vein, the beating of the heart will immediately 

 become more frequent, as I have often observed ; but 

 this cannot be caused by a more frequent heating, for 

 heating is greatly hindered by substances of that 

 kind. 



So that obviously the heart seems to be nothing 

 but a muscle, differing but little in its action from 

 other muscles, and we must believe its function to con- 

 sist in contraction alone and the expulsion of the 

 blood. 



But although nitro-aerial particles excite fermenta- 

 tion in the mass of the blood, I do not know whether 

 it is owing to the want of them that the blood, 

 immediately upon respiration being checked, becomes 

 so thick that it is quite incapable of motion, and 

 stagnates in the left ventricle of the heart. For the 

 blood while not yet impregnated with air is sent 

 readily enough from the right ventricle ; and indeed 

 the left ventricle differs from the right in no other 

 respect than in the greater power it possesses of 

 driving out the blood even if it be thicker. And yet 

 it is not to be denied that nitro-aerial particles 

 conduce not a little to the fermentation and, conse- 

 quently, also to the fluidity of the blood, as was said 

 elsewhere. But, you will ask, how is it then that 

 death follows so soon upon breathing being arrested 

 if the blood is not rendered incapable of motion ? 



