POISEUILLE 



19 



" I come to this irrevocable conclusion, that the 

 force with which a molecule of blood moves, whether 

 in the carotid, or in the aorta, etc., is exactly equal 

 to the force which moves a molecule in the smallest 

 arterial branch ; or, in other words, that a molecule 

 of blood moves with the same force over the whole 

 course of the arterial system — which, a priori, with 

 all the physiologists, I was far from thinking." 



And he adds, in a foot-note : — 



u When I say that this force is the same over 

 the whole course of the arterial system, I do not 

 mean to deny that it must needs be modified at 

 certain points of this system, which present a special 

 arrangement, such as the anastomosing arches of 

 the mesentery, the arterial circle of Willis, etc." 



Later, in 1835, he published a very valuable 

 memoir on the movement of the blood in the 

 capillaries under different conditions of heat, cold, 

 and atmospheric pressure. 



5. The Registration of the Blood-pressure. 



Poiseuille's work, in its turn, was left behind as 

 physiology went forward : especially, the discovery 

 of the vaso-motor nerves compelled physiologists 

 to reconsider the whole subject of the blood- 

 pressure. If Poiseuille's thesis (1828) be compared 

 with Marey's book (1863), Physiologie Mddicale de 

 la Circulation du Sang, it will be evident at once 

 how much wider and deeper the problem had 

 become. Poiseuille's thesis is chiefly concerned 

 with mathematics and hydrostatics ; it suggests 



