84 BIOLOGY AND ITS MAKERS 
emy of Sciences, of which he was elected a corresponding 
rember in 1697, got twenty-seven; but the lion’s share 
fell to the young Royal Society of London, which in fifty 
years—1673-1723—1received 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 
Pies observation showing the 
relation between these 
blood-vessels. This was 
perhaps his most important 
observation for its bearing 
on physiology. 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 sufficient 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. This was supplied 
by Leeuwenhoek. Fig. 20b shows one of his sketches of the 
capillary circulation. In his etforts 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 
aR 
eg e J 
ak 
Jagan Ne, 
“ a 
nt 4 
a it) 
an 
russe ea 
— 
cea Lote } 
2 Ne 
Fic. 20b.—The Capillary Circula- 
tion. (After Leeuwenhoek.) 
