LETTER 23. 14 JANUARY 1678 179 
hours I discovered in it’ so great a many of such incon- 
ceivably small creatures, that a man’s mind may not 
contain them all: and in my judgement, the sort that 
were most plentiful were much more than 1000 times 
thinner than a hair of one’s head, and 3 or 4 times as 
long as thick. These would oft-times shoot so swiftly 
forward with the hindmost part of their body, that you 
might think you saw a pike darting through the water ; 
yet each shoot was, in length, most-times about half a 
hair’s breadth. ‘The figures of the other sorts of creatures, 
whereof some were even less, I shall pass over, else 
’twould take all too long a-writing: I will only say, that 
in pepper-water, that hath stood somewhat long, I have 
oft-times seen, among the extraordinary little animalcules, 
little eels;? and the structure and the motions which 
these had, was as perfect as in big eels. But they were, 
to my eye, quite a thousand times thinner than a hair off 
one’s head ; and if a hundred of these little eels were laid 
out end to end, the whole length of them would not reach 
to the length of a full-grown one of those eels that are in 
vinegar.* 
Leeuwenhoek’s next letter in which we find any mention 
of protozoa was written in September of the same year (1678). 
It also contains some observations of whose precise signifi- 
cance I am uncertain: but it is so characteristic, and so 
clearly reveals his method of working and ways of thinking, 
that I cannot refrain from quoting it. This is what he there 
Says’: 
’ i.e., the pepper-infusion in the glass. 
* Spirilla. 
® Anguillula aceti—the “ vinegar-eel’’—which L. regarded as really a 
little fish. Large specimens measure about 1:5 mm. in length: ef. 
p. 335 infra. 
“ From Letter 26. 27 September 1678. To Nehemiah Grew. MS.Roy.Soc. 
Unpublished. (A poor contemporary English MS. translation accompanies 
the original Dutch MS.) The above is my translation of a part of the 
letter.—There is an important reference to this epistle in L.’s letters to 
Magliabechi (vide Targioni-Tozzetti, 1745: Epist.I, Vol. II, p. 345); but 
the observations on the reddening of grass are there referred to the year 
1648—which must assuredly be a misreading or misprint for 1678. 
