196 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’ 
more than a million times smaller than a coarse sand- 
grain, yet could I see very plainly that they were furnished 
with 5 joints. This appeared very strange to me, as I 
had formerly convinced myself that no water-animalcules 
proceed from such structures, and I had never conceived 
that animalcules of such littleness could live in the air. 
I took these chrysalises home, and put some of them in the 
air, to see what would come out of them; but within a 
few days, they got so dry that their former figure was 
scarce discernible ; and those which I meant to keep in 
water got lost. 
These trifles are all I have to tell you for the time 
being.’ 
The foregoing characteristic observations upon protozoa 
(or bacteria) show us an interesting picture of Leeuwenhoek 
at work—discovering new ‘‘animalcules” in new situations, 
wondering how they make their appearance and multiply in 
certain liquids, and endeavouring to account for their appar- 
ently erratic distribution. Soon afterwards he again attacked 
the problem of their generation, and sent the following account 
of his experiments : * 
When it became known to me that divers opinions 
have been expressed concerning the generation of little 
animals; and as I heard, especially, that a certain 
Gentleman’ hath writ that no living creature can be 
generated if the vessel, or bottle, in which any moisture 
or meat has been put, be tightly stoppered ; I had a mind 
to carry out some trials of this matter. 
* This sentence is in the MS. but not in the printed version. 
* From Letter 32. 14 June 1680. To Thomas Gale. MS.Roy.Soc. 
Printed in Brieven, Vol. I (Dutch) and Opera Omnia, Vol. II (Latin). No 
abstract of this letter was published in the Phil. Trans. though the letter is 
a very remarkable one. It contains, in addition to the observations here 
related, a description of yeasts obtained from beer—the first microscopic 
study of these organisms. 
* Doubtless Francesco Redi, whose celebrated treatise on “‘ the Genera- 
tion of Insects”’ first appeared in 1668. LL. could know of Redi’s work only 
by hearsay, since he was ignorant of Italian. 
