n6 Circulation of the Blood 



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 movement, 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 



