BIOGENESIS vs. ABIOGENESIS 203 



source of amusement, what he described as " little animals ob- 

 served in rain, well, sea, and snow water as also in water wherein 

 pepper had laid infused." Among other things, he observed 

 some of the larger bacteria, many protozoa, and the passage of 

 blood from arteries to veins through the capillaries; and he was 

 the first to describe, if not the discoverer of, the human spermato- 

 zoon. In one of his pubHcations, Leeuwenhoek writes as follows: 



In the year 1675 I discovered living creatures in rain-water 

 which had stood but four days in a new earthen pot, glased blew 

 within. This invited me to view this water with great attention, 

 especially those Uttle animals appearing to me ten thousand times 

 less than those represented by jMons. Swammerdam, and by him 

 called water-fleas or water-lice, which may be perceived in the 

 water with the naked eye. The first sort by me discovered in the 

 said water, I divers times observed to consist of 5, 6, 7, or 8 clear 

 globules, without being able to discover any film that held them 

 together, or contained them. When these animalcula or living 

 atoms did move, they put forth two little horns, continually moving 

 themselves; the place between these two horns was flat, though the 

 rest of the body was roundish, sharpening a little towards the end, 

 where they had a tayle, near four times the length of the whole body, 

 of the thickness (by my microscope) of a spider's web; at the end of 

 which appears a globul, of the bigness of one of those which made up 

 the body; which tayle I could not perceive, even in very clear water, 

 to be mov'd by them. These little creatures, if they chanced to 

 light upon the least filament or string, or other such particle, of 

 which there are many in the water, especially after it hath stood 

 some daj^s, they stood entangled therein, extending their body in 

 a long round, and stri\-ing to dis-entangle their tayle; whereby 

 it came to pass, that their whole body lept back towards the 

 globul of the tayle, which then rolled together serpent-like, and 

 after the manner of copper or iron-wire that, having been wound 

 about a stick, and unwound again, retains those windings and 

 turnings. This motion of extension and contraction continued a 

 while; and I have seen several hundreds of these poor little crea- 

 tures, within the space of a grain of gross sand, he cluster'd together 

 in a few filaments. 



The observations of Leeuwenhoek were greatly extended by 

 other workers during the eighteenth century, until all the more 

 important types of microscopic animals came to be recognized. 

 Although it was supposed that larger organisms arose from eggs 

 or seeds that were in the nature of living " germs," it was still pos- 

 sible to believe that micro-organisms arose spontaneously where 

 conditions were suitable for their production. This belief was not 



