Motion of the Heart and Blood 65 



in arteries filled, or in their natural state, so large a 

 quantity of blood cannot pass in so short a space of 

 time as to make any return necessary ; to all this it 

 may be answered, that from the calculation already 

 made, and the reasons assigned, it appears, that by 

 so much as the heart in its dilated state contains in 

 addition to its contents in the state of constriction, so 

 much in a general way must it emit upon each pulsa- 

 tion, and in such quantity must the blood pass, the 

 body being healthy and naturally constituted. 



But in serpents, and several fishes, by tying the veins; 

 some way below the heart, you will perceive a space 

 between the ligature and the heart speedily to become 

 empty ; so that, unless you would deny the evidence of 

 your senses, you must needs admit the return of the 

 blood to the heart. The same thing will also plainly 

 appear when we come to discuss our second position. 



Let us here conclude with a single example, con- 

 firming all that has been said, and from which every 

 one may obtain conviction through the testimony of his 

 own eyes. 



If a live snake be laid open, the heart will be seen 

 pulsating quietly, distinctly, for more than an hour, 

 moving like a worm, contracting in its longitudinal 

 dimensions, (for it is of an oblong shape,) and pro- 

 pelling its contents ; becoming of a paler colour in the 

 systole, of a deeper tint in the diastole ; and almost all 

 things else by which I have already said that the truth 

 I contend for is established, only that here everything 

 takes place more slowly, and is more distinct. This 

 point in particular may be observed more clearly than 

 the noon-day sun : the vena cava enters the heart at 

 its lower part, the artery quits it at the superior part ; 

 the vein being now seized either with forceps or between 

 the finger and thumb, and the course of the blood for 

 some space below the heart interrupted, you will preceive 

 the part that intervenes between the fingers and the 

 heart almost immediately to become empty, the blood 



