A HISTORY OF SCIENCE 



section as practised to-day, that by the sacrifice of a 

 single deer in the cause of science Hunter discovered 

 a fact in physiology that has been the means of saving 

 thousands of human lives and thousands of human 

 bodies from needless mutilation. We refer to the dis- 

 covery of the "collateral circulation" of the blood, 

 which led, among other things, to Hunter's successful 

 operation upon aneurisms. 



Simply stated, every organ or muscle of the body is 

 supplied by one large artery, whose main trunk dis- 

 tributes the blood into its lesser branches, and thence 

 through the capillaries. Cutting off this main artery, 

 it would seem, should cut off entirely the blood-supply 

 to the particular organ which is supplied by this vessel ; 

 and until the time of Hunter's demonstration this be- 

 lief was held by most physiologists. But nature has 

 made a provision for this possible stoppage of blood- 

 supply from a single source, and has so arranged that 

 some of the small arterial branches coming from the 

 main supply-trunk are connected with other arterial 

 branches coming from some other supply - trunk. 

 Under normal conditions the main arterial trunks 

 supply their respective organs, the little connecting 

 arterioles playing an insignificant part. But let 

 the main supply -trunk be cut off or stopped for 

 whatever reason, and a remarkable thing takes 

 place. The little connecting branches begin at once 

 to enlarge and draw blood from the neighboring un- 

 injured supply - trunk. This enlargement continues 

 until at last a new route for the circulation has been 

 established, the organ no longer depending on the now 

 defunct original arterial trunk, but getting on as well 



82 



