210 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’ 
animals aforesaid devoured them, methought this a 
sufficient reason why freshwater mussels are not found in 
ereater plenty.’ 
After this, I let the water stand for twelve more days, 
without replenishing it, in order to see whether, if I did 
so, the animalcules would multiply in greater numbers. 
But I perceived that the animalcules decreased from day 
to day; so that by the 8th of October they were indeed 
grown so few, that where I had before discovered a good 
hundred of them, I now could scarce see one; and those 
of the biggest sort, which still remained over, moved 
forward very slow, and were very thin in the body; and 
all the little shells of the unborn mussels had so far 
increased in transparency, that I could make out some 
hundreds of very little parts, whereof they were composed. 
And so, from all these observations, I concluded that 
all the various animalcules had now died for lack of food. 
In order to satisfy myself further concerning the 
plentevous multiplication of the little animalcules, and 
in so very short a time, I took a parcel of canal-water, 
somewhat more than a common wine-glass full, and put 
in it an ordinary mussel, that I had taken out of its shell’ ; 
and I put this mussel in the water to see, if ’twere 
possible, whether the animalcules would multiply beyond 
what they commonly do, owing to the food that they 
would be able to get from the mussel. 
After the mussel had lain for four-and-twenty hours in 
the water, I took a little of the uppermost part of the 
water, and examined it through the microscope; and I 
' From these observations one can hardly doubt that L. had got 
something more than an inkling of the part played by putrefactive micro- 
organisms in the general oeconomy of nature. To appreciate the novelty 
of this notion—nowadays commonplace— one must remember that it belongs, 
historically, to the nineteenth century. 
? In such an infusion of freshwater mussel many different Protozoa are 
commonly found, including ciliates (e.g., Paramecium) and flagellates (e.g., 
Trepomonas). For this reason it is impossible to determine what particular 
forms L. was likely to have seen. 
