THE HISTORY OF BACTERIOLOGY. 51 



these also were living or not, but I was unable to recognize 

 even the slightest movement as a sign of life." 



In the material taken from the teeth of an old man who never cleaned 

 his teeth, Leeuwenhoek found an inconceivable number of living animalcule 

 which darted about more quickly than any he had ever seen before ; "the 

 largest were present in very great numbers, and waved about by the 

 locomotion of their bodies. Besides these, other animalculae were present 

 in such large numbers that the whole water seemed to be alive." 



This admirable account really contains the first accurate 

 description of the rod-shaped bacteria, motile and motionless, 

 of longer threads or bacilli, of the spiral threads or spirilla, 

 and of rounded micro-organisms or micrococci. It was con- 

 siderably improved upon in a letter to the Royal Society, 

 dated October i, 1692, in which he speaks of small rounded 

 animalculae,the diameter of which is a thousand times less than 

 that of a fine grain of sand ; of organisms having a somewhat 

 greater diameter than the round ones, and being five or six 

 times as long as they were broad, equally thick throughout 

 their whole length, and which moved slowly backwards and 

 forwards through a bending of their bodies. Along with 

 these he describes what are evidently spirilla, with their 

 characteristic movements, " a few organisms about the same 

 length or slightly longer, which moved their bodies in 

 comparatively marked curves, swam forwards or backwards, 

 or twisted themselves in an extremely lively fashion." He 

 also observed still longer and more sluggish organisms, 

 sometimes straight and sometimes bent. 



Although Leeuwenhoek did not attempt to theorize as to 

 the meaning of the presence of these organisms in the 

 mouth, we find that, in 1713, after finding similar organisms 

 in the greenish pellicle formed on the surface of the water 

 in an aquarium, he came to the conclusion that the organ- 

 isms seen on the teeth found their way into the mouth 

 through the medium of the drinking-water that had been 

 stored in barrels, and that some of these found there a nidus 

 in which they might multiply. 



The world that Leeuwenhoek thus opened up so 

 thoroughly was rapidly invaded by other observers and 

 theorists. The thoughtful physicians of the time believed 

 that at last they had found the fons et ortgo mati, and 

 Nicolas Andry, reviewing Kircher's "Contagium Ani- 

 matum," replaced his worms by these newly-described 



