226 LEEUWENHOEK AND HIS “ LITTLE ANIMALS” 
perhaps imagine that these animalcules, because of their 
extreme littleness, might well get through into our blood ; 
but I conceive that the vessels which conduct the material 
(out of which blood, fat, etc. is made) are so small, or must 
pass through such narrow channels, that even if such a 
little animalcule were divided into more than 1000 parts, 
‘twould still be too big to get through them.’ 
I have, moreover, examined my excrement when it was 
of ordinary thickness, and also mixed with clean water, 
but could then discover no animalcules in it; but 
whenever the stuff was a bit looser than ordinary, I have 
still seen animalcules therein, contrary to my expectation. 
I have, however, also seen in it some particles of food that 
were not digested; among others, for example, after I had 
eaten asparagus I saw very prettily its little tubes (off 
which the soft parts had been all digested away). 
At divers times in the summer I have betaken myself 
into our meadows, and collected the dirt of cows and 
horses, just as they let it drop; yet I could discover no 
living animalcules therein, but most of this stuff (setting 
aside grass-particles which were undigested) was made up 
of globules, whereof 6 would be as big as a blood-globule, 
and many lesser globules of which I judged that 36 
together would be only as big as a blood-globule; all these 
lying in a clear medium. 
In the month of May,’ I rode my horse (which is a 
mare) very hard, for about 1% hour’s going;° and on 
getting back to the stable, she let go her urine; and as 
the last of this urine looked to me very thick, and was 
" L. means that the channels—in the intestinal wall—through which 
the ultimate food-particles in the gut pass into the blood-stream are too 
minute for bacteria to traverse them: and that even if a bacterium were 
but a tenth of its length, it still would be too big to do so. 
> Presumably anno 1681. 
* 14 wre gaens MS. The printed version says “an hour and a quarter ’ 
(een en een quart van een ure). Apart from this discrepancy in the time, it 
should be noted that L. does not mean that he rode his mare hard for an 
hour and a half (a pretty strenuous feat), but for a distance equal to that 
y 
