LETTER 71. 7 MARCH 1692 205 
In Leeuwenhoek’s next communications we find no further 
mention of either protozoa or bacteria until we come to his 
Letter 71, which, while recording various other observations, 
contains the following words: ' 
I have by me the following notes, which I feel 
constrained to add. 
For several days past I have kept in a clean glass, in 
my closet, some rain-water, gotten from a rain-cistern ; 
in which water there was a little red worm,’ which I 
divers times observed, by reason of its curious structure. 
In this water, after a day or two, a multitude of little 
living creatures did propagate themselves, they being of 
two sorts which you commonly find in fresh or sweet 
waters. The bigger sort I judged to be so small, that 
thirty thousand of them together would scarce make up a 
body as big as a coarse grain of sand. 
On several different days I did look upon these little 
animals,* and for so long, that not alone my eyes, but my 
very hands, got a-weary ; and this was simply because I 
did perceive such a plenty of these little animals, which 
were coupled together, and so long remained in this pos- 
ture: and I observed how the bigger sort dragged the 
little ones along, or swam forward with them, with the 
help of very plentevous feet, wherewith these animals are 
furnished withal ; so that 1 was thus able on this occa- 
sion to observe the copulation of these little animals 
clearer than ever before. Nay, I saw them as plain as 
you can see flying creatures* a-copulating before your 
naked eye. 
* Letter 71. 7 March 1692. To the Royal Society. MS.Roy.Soc. 
Printed in Brieven, Derde Vervolg, p. 396 (the passage here translated 
beginning on p. 423): Opera Omnia, Vol. II, p. 239 (1st pagination). A 
partial English translation was also published in Phil. Trans. (1694), 
Vol. XVIII, No. 218, pp. 194-199; but the passage here given in full is 
there so abridged that it occupies only 84 lines (on p. 198). 
> Rvidently a “ blood-worm’”’ (larva of Chironomus). 
* The animals referred to are evidently ciliates. 
* i.e. insects—not birds. 
