138 Circulation of the Blood 



ties of its derivative branches ; and indeed, if the 

 experiment which Galen recommends were properly 

 performed by any one, its results would be found in 

 opposition to the views which Vesalius believed they 

 would support. 



But we do not therefore deny everything like motion 

 to the tunics of the arteries ; on the contrary, we allow 

 them the same motions which we concede to the heart, 

 viz. a diastole, and a systole or return from the distended 

 to the natural state; this much we believe to be effected 

 by a power inherent in the coats themselves. But it is 

 to be observed, that they are not both dilated and con- 

 tracted by the same, but by different causes and means ; 

 as may be observed of the motions of all parts, and of 

 the ventricle of the heart itself, which is distended by 

 the auricle, contracted by its own inherent power ; 

 so, the arteries are dilated by the stroke of the heart, 

 but they contract or collapse of themselves. 1 



You may also perform another experiment at the 

 same time : if you fill one of two basins of the same size 

 with blood issuing per saltum from an artery, the other 

 with venous blood from a vein of the same animal, you 

 will have an opportunity of perceiving by the eye, both 

 immediately and by and by, when the blood in either 

 vessel has become cold, what differences there are 

 between them. You will find that it is not as they 

 believe who fancy that there is one kind of blood in 

 the arteries and another in the veins, that in the 

 arteries being of a more florid colour, more frothy, 

 and imbued with an abundance of I know not what 

 spirits, effervescing and swelling, and occupying a 

 greater space, like milk or honey set upon the fire. 

 For were the blood which is thrown from the left 

 ventricle of the heart into the arteries, fermented into 

 any such frothy and flatulent fluid, so that a drop or 

 two distended the whole cavity of the aorta ; unques- 



1 Vide Chapter III. of the Disquisition on the Motion of the Heart 

 and Blood. 



