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CHAPTER 3 
THE FIRST OBSERVATIONS ON ENTOZOIC 
PROTOZOA AND BACTERIA 
(Lerters 7, 33, 34, 38, 39, 75, 110, etc.) 
E have already seen (in Chapter 1) how Leeuwenhoek 
NV discovered the free-living Protozoa and Bacteria. 
We inust now chronicle his discoveries in the world 
of similar “ parasitic’ organisms.’ 
It will be remembered that Leeuwenhoek first saw protozoa 
in water in the summer of 1674.* He probably first saw a 
parasitic protozoon—though he had no idea what it was—in 
the autumn of the same year. Whilst examining the bile of 
various animals, he hit upon some curious structures which he 
described, in the course of a rather rambling letter, in the 
following terms: * 
The bile of a cow was examined* by me on the Ist 
instant,’ and therein I beheld some few globules” that 
floated in the liquid ; but I didn’t see them unless I set the 
bile in a continual motion before my sight, for ’twould else 
have been impossible for me to perceive the globules in it, 
* To call all such micro-organisms studied by L. by the opprobrious 
name of © parasite” is hardly justifiable, for most of the forms which he 
described cannot be regarded as harmful. They are “ parasitic” in a 
colloquial and unscientific sense only. 
” See p. 109. 
> From Letter 7. 19 October 1674. To Oldenburg. MS.Roy.Soc. 
This letter was wholly unpublished until recently, when I first published 
(Dobell, 1922) the passages given here in revised translation. 
* i.e., with the microscope. 
° 4.e., 1 October 1674. 
° clootgens MS. 
