6 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS” 
My own chief interest in Leeuwenhoek has always been in 
his observations on protozoa and bacteria—as I have already 
told you. But this is because these “ little animals’ (as he 
called them) have engaged my own attention all my life, being 
the favourite objects of my own researches. His own tastes 
were more catholic : indeed, he studied almost everything that 
can be looked at through a lens, and thereby found out some- 
thing new about it too. His inquisitiveness was insatiable, and 
his discovery of the Protozoa and the Bacteria was merely an 
incident in a life crowded with discovertes—real and imaginary. 
For example, Leeuwenhoek’s observations on insects, rotifers, 
and a host of other ‘‘animalcules,”’ are equally remarkable ; 
his researches on blood-corpuscles and the capillary circulation 
are already classics; his comparative studies of spermatozoa 
now stand as a landmark in the History of Biology; his dis- 
covery of parthenogenesis (in aphids) and of budding im an 
animal (Hydra) are too notorious almost for comment : while 
his other investigations in anatomy, histology, physiology, em- 
bryology, zoology, botany, chemistry, crystallography, and 
physics, only await editors for their proper appreciation. He 
made the maddest experiments, and attempted to see things that 
nobody would now even dream of seeing. I imagine, for instance, 
that nobody before (or after) Leeuwenhoek ever thought of 
watching the explosion of gunpowder under the microscope - yet 
he devised an apparatus for this purpose, and though he nearly 
blinded himself he succeeded in seeing what he wanted. And 
he actually discovered protozoa and bacteria in organic infusions 
in the course of a crazy attempt to find out, by the microscopic 
examination of macerated peppercorns, why pepper ts hot ! 
But these are only a few of Leeuwenhoek’s astonishing 
doings, and I need say nothing further about them here. In 
the pages which follow I merely attempt to assemble and edit 
all his observations on protozoa and bacteria. Originally I 
collected—simply for my own information and pleasure—every- 
thing that I could find on these matters, both published and 
unpublished, in his extant writings. I had no thought of 
making a book for others to read. Yet after a time I found 
that I had amassed a body of records which seemed to me so 
surprisingly great and original, that I felt it my duty to share 
my findings with other protozoologists and bacteriologists : so 
my own private notes gradually grew into the work now before 
you. 
