LETTERS 6 AND 13 EEE 
with green and very glittering little scales; others again 
were green in the middle, and before and behind white’ ; 
others yet were ashen grey. And the motion of most of 
these animalcules in the water was so swift, and so 
various, upwards, downwards, and round about, that ’twas 
wonderful to see: and I judge that some of these little 
creatures were above a thousand times smaller” than the 
smallest ones I, have ever yet seen,’ upon the rind of 
cheese, in wheaten flour, mould, and the like. 
No further observations on these ‘little animals” appear 
to have been reported until more than a year later. But in a 
letter written in December, 1675, Leeuwenhoek again alludes 
to them briefly, in the following words :* 
In the past summer I have made many observations 
upon various waters, and in almost all discovered an 
abundance of very little and odd animalcules, whereof 
some were incredibly small, less even than the animalcules 
which others have discovered in water, and which have 
been called’ by the name of Water-flea, or Water-louse. 
This passage is important as establishing the date when 
some of Leeuwenhoek’s earliest observations were made—the 
summer of 1675. At this time, however, he gave no more 
detailed account of his discoveries: but he kept a careful 
record, and a month later the following passage occurs in a 
further note to Oldenburg :° 
* Probably Euglena viridis. The peculiar arrangement of the chromato- 
phores in this species gives the flagellate this appearance under a low 
magnification. The identification seems to me almost certain; and, if 
correct, this is the first mention of Huglena, whose discovery is usually 
attributed to Harris (1696). 
> i.e., in volume—not in linear dimensions. 
* i.e., mites. 
* From Letter 13. 20 December 1675. MS.Roy.Soc. Unpublished. 
Original in Dutch. 
* By Swammerdam. See note 1 on p. 118. 
° From Letter 13a. 22 January 1676. MS.Roy.Soc. Unpublished. 
Original in Dutch. 
