JOHN HUNTER 



15 



When it was at its full height, it would rise and 

 fall at and after each pulse 2, 3, or 4 inches, and 

 sometimes it would fall 12 or 14 inches, and have 

 there for a time the same vibrations up and down, 

 at and after each pulse, as it had when it was at its 

 full height, to which it would rise again, after forty 

 or fifty pulses." 



3. The Collateral Circulation. 



After Hales, came John Hunter, who was five 

 years old when the Statical Essays were published. 

 His experiments on the blood were mostly con- 

 cerned with its properties, not with its course ; but 

 one great experiment must be noted here that puts 

 him in line with Harvey, Malpighi, and Hales. He 

 got from it his knowledge of the collateral circula- 

 tion ; he learned how the obstruction of an artery is 

 followed by enlargement of the vessels in its neigh- 

 bourhood, so that the parts beyond the obstruction 

 do not suffer from want of blood : and the facts of 

 collateral circulation were fresh in his mind when, a 

 few months later, he conceived and performed his 

 operation for aneurysm (December, 1785). The 

 "old operation" gave him no help here; and "Anel's 

 operation " was but a single instance, and no sure 

 guide for Hunter, because Anel's patient had a 

 different sort of aneurysm. Hunter knew that the 

 collateral circulation could be trusted to nourish 

 the limb, if the femoral artery were ligatured in 

 "Hunter's canal" for the cure of popliteal aneu- 

 rysm ; and he got this knowledge from the 

 experiment that he had made on one of the deer 



