CIRCULATION OF THE BLOOD. 93 



the aorta disgorging itself into the ventricle, precisely as the ven- 

 tricle has disgorged itself into the aorta. There would thus be 

 circulation neither in the heart nor in the mesentery, but an 

 alternate flux and reflux, a useless labour, as it seems. If, 

 therefore, and for the reason assigned and approved by him, a 

 circulation through the heart be argued for as a thing necessary, 

 the argument has precisely the same force when applied to 

 the mesentery : if there be no circulation in the mesentery, 

 neither is there any in the heart ; for both affirmations, this in 

 reference to the heart, that in reference to the mesentery, 

 merely changing the words, stand or fall together, by force of 

 the very same arguments. 



He says : " The sigmoid valves prevent regurgitation into 

 the heart ; but there are no valves in the mesentery." To this 

 I reply, that the thing is not so ; for there is a valve in the 

 splenic vein, and sometimes also in other veins. And besides, 

 valves are not met with universally in veins ; there are few or 

 none in the deep-seated veins of the extremities, but many in 

 the subcutaneous branches. For where the blood is flowing 

 naturally from smaller into greater branches, into which it is 

 disposed to enter, the pressure of the circumjacent muscles is 

 enough, and more than enough to prevent all retrograde move- 

 ment, and it is forced on where the way lies open ; in such 

 circumstances, what use were there for valves? But the 

 quantity of blood that is forced into the mesentery by each 

 stroke of the heart, may be estimated in the same way as 

 you estimate the quantity impelled into the hand when you 

 bind a ligature with medium tightness about the wrist: if in 

 so many beats the vessels of the hand become distended, and 

 the whole extremity swells, you will find, that much more than 

 a single drop of blood has entered with each pulse, and which 

 cannot return, but must remain to fill the hand and increase 

 its size. But analogy permits us to say, that the same thing 

 takes place in reference to the mesentery and its vessels, in an 

 equal degree at least, if not in a greater degree, seeing that the 

 vessels of the mesentery are considerably larger than those of 

 the carpus. And if any one will but think on the difficulty 

 that is experienced with all the aid supplied by compresses, 

 bandages, and a multiplied apparatus, in restraining the flow of 

 blood from the smallest artery when wounded, with what force 



