‘cé 
12 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’ 
The living creatures discovered by me in water, were 
in ordinary rain-water, that was caught from a pantile 
roof’ in stone troughs under the ground, or in tubs; also 
in well or spring water, coming up through well-sand ; 
likewise in the canal water, that runneth through this 
Town and through the country. Upon these I have 
made divers notes, concerning their colour, figure, the parts 
whereof their body is composed, their motion, and the 
sudden bursting of their whole body; of which notes I 
keep a copy by me, which I shall send you at the earliest 
opportunity. 
The promised ‘“ notes”? were sent in due course: they form 
the celebrated letter (Letter 18) which protozoologists have 
long regarded as the first paper ever written upon the objects 
of their special study. Moreover, this letter also contains the 
first account ever written of the Bacteria, as well as many 
other original observations. In view of its unique interest, 
therefore, I must say a few further words of introduction at 
this point. 
Leeuwenhoek’s 18th Letter. 
The famous “ Letter on the Protozoa” is a truly amazing 
document. According to my reckoning it is Leeuwenhoek’s 
eighteenth scientific epistle to the Royal Society, and I shall 
therefore refer to it henceforward simply as Letter 18. The 
original Letter itself is preserved among the Royal Society’s 
manuscripts, and is still—except for a few slight mutilations— 
intact. It is in Dutch, and covers 17} folio pages, closely 
written in a neat small hand which is not Leeuwenhoek’s own, 
though the manuscript has been carefully corrected by him 
throughout (in a different ink), and bears his autograph 
signature at the end. It seems likely that he wrote the letter 
himself, with his notebook before him, and then caused his 
1 The water so collected was probably very clean water: for Dutch 
houses then—as now—were wont to be kept clean both inside and out. 
John Ray, in the diary of his Travels—writing in 1663—notes that, in the 
Netherlands, ‘‘all things both within and without” were “ marvellously 
clean, bright, and handsomly kept: nay some are so extraordinarily curious 
as to take down the very Tiles of their Pent-houses and cleanse them.” 
Vide Ray (1673), p. 52. 
