POISEUILLE 



17 



seen or expected. A new property of the living 

 arteries was unfolded to him." 



All the anatomists had overlooked this physio- 

 logical change in the living body, brought about by 

 disease. And the surgeons, since anatomy could 

 not help them, had been driven by the mortality of 

 the "old operation" to the practice of amputation. 



4. The Mercurial Manometer. 



Hale's experiments on the blood-pressure were 

 admirable in their time ; but neither he nor his 

 successors could take into account all the physio- 

 logical and mathematical facts of the case. But a 

 great advance was made in 1828, when Poiseuille 

 published his thesis, Sur la Force du Cceur Aorttque, 

 with a description of the mercurial manometer. 

 Poiseuille had begun with the received idea that the 

 blood-pressure in the arteries would vary according 

 to the distance from the heart, but he found by 

 experiment that this doctrine was wrong : — 



''At my first experiments, wishing to make sure 

 whether the opinions, given a priori, were true, I 

 observed to my great astonishment that two tubes, 

 applied at the same time to two arteries at different 

 distances from the heart, gave columns of exactly 

 the same height, and not, as I had expected, of 

 different heights. This made the work very much 

 simpler, because, to whatever artery I applied the 

 instrument, I obtained the same results that I 

 should have got by placing it on the ascending 

 aorta itself." 



B 



