An AbJiraSi of 0 Letter of Mr. Leeuwenhoeck 
Fellow of the R. Socitty ^dated March ^oth* 1685. 
to the R. S. Concerning Generation by an In- 
Bout the latter end of the Summer of the year 
X\ 1(583. \ took x\\^Sem $71 Mafculum oisiDog, which 
was of about a year and half old. This I put into a 
Glafspipe, and wrapt it up in foft leather, becaule the 
nights wei^e fomething cold. This Semen I obferved 4 
days lucceffively, and in the firft, I found that feveralt 
of its Animals were dead. In the 2d and 3d day, there 
were yet more of them dead, but on the 4 th, there were 
very few left alive ; and fo far I proceeded at that time. , 
But in the beginning of (?Sd?^^r in the year 1^84. I ob- 
ferved again the Semen Ma/culum of the fame Dog, who 
was then very ftrong and Vigorous, and I found that afr 
ter 7 days and nights, there were fome few Animals yet 
left alive ; a very few whereof fwam as briskly as if they 
had jufk come from the Dog, 
From hence I inferr, that thefe Animals, would hav« 
lived a much longer time, if they had been in the Zterm: 
alio that Conception in F^;;2^/^j is not always made 
mediate pojl congrejpim, hut iom^timts 9, or io> or more 
days after it, if one of the Animals can then find the 
'FunUum or proper place for its Nourifliment ; and laftly 
that the Vterus may not be fit for the Reception of Ani- 
mals at one time, tho' before 2 or 3 days are paft, it may 
become perfectly capable. 
I know my Opinion about Generation has been rejed:- 
ed by feveral perlons, fome whereof being skilled in A- 
natomy have afBrmed to me, thit t)ie SemeWMafiulum 
never comes into the Vterus; that its never to be feen 
in that place; and that its nothing but a Fapour which', 
caufes fruitfullnefs. But I am not of thefe mens minds; 
for it fedms plain to me, that the parts are proportioned: 
W 
