494 
DR. PHILIP ON THE POWERS ON WHICH 
head, and the animal was so placed that the vein was brought into the per- 
pendicular position, the head of the animal being undermost, so that it was 
necessary for the vein, in conveying the blood to the heart, to convey it per- 
pendicularly against its gravity. The ligature, which was placed at what was 
now the lowest part of the exposed portion of the vein, was suddenly tightened, 
while Mr. Cutler and myself observed the vessel. The blood in the part of 
the vein between the ligature and the heart was instantly and completely ex- 
pelled, as the transparency of the vessel enabled us to perceive. The vessel 
itself wholly collapsed, proving that all its blood had entered the heart, so that 
to a superficial view there seemed to be no vessel in the part where a large 
dark-coloured vein had just before appeared. In the mean time, on the other 
side of the ligature, the vein had become gorged with blood. 
In the foregoing experiment we see the blood rising rapidly against its 
gravity, where all causes external to the vessel on which the venous part of 
the circulation has been supposed to depend, had ceased to exist, and the vis 
& tergo was wholly destroyed by the ligature. 
By a similar experiment, the power of the arteries in propelling the blood 
may also be demonstrated. 
Exp. — In a newly dead rabbit, the circulation being supported by artificial 
breathing, the carotid artery was laid bare for about an inch and a half. The 
animal was so placed as to keep the vessel in the perpendicular position, the 
head being now uppermost. A ligature was passed behind that part of the 
vessel which was next the heart, and Mr. Cutler and myself observed the 
vessel at the moment the ligature was tightened. The artery of course did 
not collapse as the vein had done in the preceding experiment ; but the blood 
was propelled along the vessel, so that it no longer appeared distended with it. 
It was at once evident, from the change of appearance in the vessel, that the 
greater part of the blood had passed on in a direction perpendicularly opposed 
to its gravity. It is worthy of remark, that the blood of the artery was pro- 
pelled neither so rapidly nor so completely as that of the vein, the cause of 
which will be evident in the observations I am about to make on the nature 
of the function and powers of these vessels. 
When the whole of the preceding facts are considered, it will, I think, be 
admitted that the circulation is performed by the combined power of the heart 
