602 LETTERS. 



stance. For if the aorta be tied near the left ventricle of the 

 heart in a living animal, and all the blood removed from the 

 arteries, the veins are still seen full of blood ; so that it neither 

 moves back spontaneously into the arteries, nor can it be 

 repelled into these by any force, whilst even in a dead animal 

 it nevertheless falls of its own accord through the finest pores 

 of the flesh and skin from superior into inferior parts. The 

 passage of the blood into the veins is, indeed, effected by the 

 impulse in question, and not by any dilatation of these in the 

 manner of bellows, by which the blood is drawn towards them ; 

 but there are no anastomoses of the vessels by conjunction (per 

 copulam), in the way you mention, none where two vessels 

 meeting are conjoined by equal mouths. There is only an 

 opening of the artery into the vein, exactly in the same man- 

 ner as the ureter opens into the bladder (and the biliary duct 

 opens into the jejunum), by which, whilst the flow of urine is 

 perfectly free towards the bladder, all reflux into the smaller 

 conduits is effectually prevented; the fuller the bladder is, in- 

 deed, the more are the sides of the ureters compressed, and 

 the more effectual is all ascent of urine in them prevented. 

 Now, on this hypothesis, it is easy to render a reason for the 

 experiment which I have already mentioned. I add further, 

 that I can in nowise admit such anastomoses as are commonly 

 imagined, inasmuch as the arteries being always much smaller 

 than the veins, it is impossible that their sides can mutu- 

 ally conjoin in such a way as will allow of their forming a 

 common meatus ; it seems matter of necessity that things 

 which join in this way should be of equal size. Lastly, these 

 vessels having made a certain circuit, must, at their termina- 

 tions, encounter one another; they would not, as it happens, 

 proceed straight to the extremities of the body. And the 

 veins, on their part, if they were conjoined with the arteries 

 by mutual inosculations, would necessarily, and by reason of 

 the continuity of parts, pulsate like the arteries. 



And now, that I may make an end of my writing,* I say, 

 that whilst I think the industry of every one deserving of 

 commendation, I do not remember that I have anywhere be- 

 praised mine own. You, however, most excellent sir, I conceive 

 have deserved high commendation, both for the care you have 

 bestowed on your disquisition on the liver of the ox, and for the 



