84 



BIOLOGY AND ITS MAKERS 



emy of Sciences, of which he was elected a corresponding 

 racmber in 1697, got tweni y-seven ; but the lion's share 

 fell to the young Royal Society of London, which in fifty 

 years — 1673-1723 — received 375 letters and papers." " The 

 works themselves, except that they lie in the domain of 

 natural history, are disconnected and appear in no order 

 of systematized study. The philosopher was led by what 

 transpired at any moment to lead him." 



The Capillary Circulation. — In 1686 he observed the 

 minute circulation of the blood, and demonstrated the capil- 

 lary connection between arteries and veins, thus forging the 



final link in the chain of 

 observation showing the 

 relation between these 

 blood-vessels. This v.as 

 perhaps his most important 

 observation for its bearing 

 on physiolog}'. It must be 

 remembered that Harvey 

 had not actually seen the 

 circulation of the blood, 

 which he announced in 

 1628. He assumed on en- 

 tirely sufi'icient grounds the 

 existence of a complete cir- 

 culation, but there was 

 wanting in his scheme the 

 direct ocular proof of the 

 passage of blood from arteries to veins, lliis was supplied 

 by Leeuwenhoek. Fig. 2oh shows one of his sketches of the 

 capillary circulation. In his efi'orts to see the circulation 

 he tried various animals; the comb of the young cock, the 

 ears of white rabbits, the membraneous wing of the bat were 

 progressively examined. The next advance came when he 





in A ' 







rf 



n 



Fig. 206. — The Capillary Circula' 

 tion. (After Leeuwenhoek.) 



