ANAEROBIC BACTERIA DISCOVERED 199 
Leeuwenhoek discovered that organisms could live and 
multiply under the hemi-anaerobic conditions present in his 
closed tube, he was unable at that time, of course, to realize 
the full importance of his discovery. I have also confirmed 
the foregoing observations, though I made no attempt to 
determine exactly what species of bacteria were present in 
the tubes—being satisfied with Prof. Beijerinck’s authoritative 
opinion. Iam also satisfied that no protozoa can usually be 
obtained in experiments such as the above if the procedure 
described be adhered to. 
It seems remarkable that Leeuwenhoek—always a vigorous 
opponent of the doctrine of spontaneous generation—appears 
to have made no further study of the very interesting pheno- 
mena which the foregoing experiments record. He must 
have been puzzled, at first, to account for the appearance of 
bacteria in his sealed tube: but I think his own words supply 
the explanation which occurred to him, and which apparently 
satisfied him at that time. In previous letters’ he makes the 
suggestion that ‘“‘ animalcules” or their “ seeds ”’ are present, 
or can exist, in rain—being drawn up into the clouds with 
the water in which they live or are formed, and subsequently 
scattered when the rain falls. Consequently, he probably 
imagined that the rain-water introduced into the sealed tube 
already contained ‘“ animalcules” —or “seeds”? capable of 
germinating into “animalcules”»—-which found sufficient 
‘air’ in the tube to enable them to live and breathe and 
multiply for at least some days. Nearly a hundred years 
subsequently elapsed before any further light was shed on this 
subject by the ingenious experiments of Spallanzani, though 
it was not until much later that the problem was solved— 
more or less completely—by Pasteur and Tyndall. Redi’s 
famous observations by no means solved the problem of 
spontaneous generation—as is often lightly stated: and this 
point is clearly brought out by Leeuwenhoek’s experiment, as 
he himself apparently realized; though he made no attempt— 
or, at least, recorded none—to push his inquiries any further. 
A few months after he had written the foregoing letter to 
Dr Gale, Leeuwenhoek wrote again to Dr Hooke: and in 
" Cf. Letter 18 (p. 163) and Letter 31 (p. 194). 
