INTESTINAL PROTOZOA OF MAN DISCOVERED 225 
I have also seen a sort of animalcules that had the 
figure of our river-eels: these were in very great plenty, 
and so small withal, that I deemed 500 or 600° of ’em 
laid out end to end would not reach to the length of a full- 
grown eel such as there are in vinegar.” These had a 
very nimble motion, and bent their bodies serpent-wise, 
and shot through the stuff as quick as a pike does through 
the water.’ 
At another time I saw, in 4 several observations, but 
one animalcule of the sort first spoken of;* but at my 
fourth observation, observing more narrowly than before, 
I saw a great number of animalcules,’ each of which I 
judged to be more than 200 times less than a globule of 
our blood: for I imagined that I could make out that the 
length of six diameters of one animalcule couldn’t reach 
beyond the diameter of one blood-globule. But here I 
speak to those who are versed in geometry, and know full 
well that if the diameter of one body be 1 and that of 
another (of like figure) be 6; then the difference in their 
bulk is as 1 to 216. And I can’t forbear to say that I 
have divers times judged that I have seen, with great 
delight, in a particle of matter of the bigness of a coarse 
sand-grain, more than 1000 living animalcules, and these 
of 3 or 4 sorts, all alive together; nay, you might well 
have supposed that the whole material consisted of nought 
but living animalcules. Some people hearing this might 
cme EUS USSU 
* The Latin version wrongly says “50 or 60” (quinquaginta aut 
secaginta), which would—if correct—-put a very different complexion on 
this passage. 
> Anguillula aceti, the “ vinegar-eel’’. Cf. p. 150 swpra. 
? From the description here given, it can hardly be doubted that these 
organisms were spirochaetes. In recent years a vast literature has sprung 
up on the intestinal species in man; but it must suffice to note here that 
more than one species occurs in human faeces, and that spirochaetes of 
some sort are normally present in the intestines of most human beings. 
This is the first record of their occurrence. 
* Referring to Giardia. 
> Probably bacteria, but possibly inanimate particles in Brownian 
movement. 
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