54 DESCARTES. 



alone, and from the heat which may be felt with the 

 fingers, and from the nature of the blood as learned 

 from experience, as does the motion of a clock from 

 the power, the situation, and shape of its counter- 

 weights and wheels. 



But if it be asked how it happens that the blood in 

 the veins, flowing in this way continually into the 

 heart, is not exhausted, and why the arteries do not 

 become too full, since all the blood which passes 

 through the heart flows into them, I need only men- 

 tion in reply what has been written by a physician* 

 of England, who has the honour of having broken 

 the ice on this subject, and of having been the first 

 to teach that there are many small passages at the 

 extremities of the arteries, through which the blood 

 received by them from the heart passes into the 

 small branches of the veins, whence it again returns 

 to the heart ; so that its course amounts precisely to 

 a perpetual circulation. Of this we have abundant 

 proof in the ordinary experience of surgeons, who, 

 by binding the arm with a tie of moderate strait- 

 ness above the part where they open the vein, cause 

 the blood to flow more copiously than it would have 

 done without any ligature ; whereas quite the con- 

 trary would happen were they to bind it below ; that 

 is, between the hand and the opening, or were to 

 make the ligature above the opening very tight. 

 For it is manifest that the tie, moderately strait- 

 ened, while adequate to hinder the blood already in 

 the arm from returning towards the heart by the 

 veins, cannot on that account prevent new blood 



* Harvey Lat. Tr. 



