so BACTERIA. 



to place before the Royal Society of London a series of 

 most interesting and valuable letters giving the result of his 

 researches on minute specks of living protoplasm. The 

 results of these observations are fully detailed in his collected 

 works. 



Towards the end of 1675 he discovered in water, in an 

 infusion of pepper, in the intestinal canals of horses, flies, 

 frogs, pigeons, fowls, and even in his own diarrhoea stools, 

 small moving and living forms of such extreme minuteness 

 that other observers with the best apparatus they had at 

 command, even with the accurate and lucid description he 

 gave, could not for long confirm his results. It was not, 

 however, until 1683 that he actually described and depicted 

 minute organisms in material taken from the teeth, that 

 we can at present recognize from his descriptions and 

 drawings as bacteria. Describing them, he says : " I saw 

 with very great astonishment, especially in the material 

 mentioned, that there were many extremely small animals 

 which moved about in a most amusing fashion ; the largest 

 of these" (represented by him in an admirable figure) 

 " showed the liveliest and most active motion, moving 

 through rain-water or saliva like a fish of prey darts through 

 the water ; this form, though few in actual numbers, was 

 met with everywhere. A second form moved round, often 

 in a circle, or in a kind of curve ; these were present in 

 greater numbers. The form of a third kind I could not 

 distinguish clearly ; sometimes it appeared oblong, some- 

 times quite round. They were very tiny, in addition to 

 which they moved forward so rapidly that they tore through 

 one another : they presented an appearance like a swarm of 

 midges and flies buzzing in and out between one another. 

 I had the impression that I saw several thousands in a 

 single drop of water or saliva which was mixed with a 

 small part of the above-named material not larger than a 

 grain of sand, even when nine parts of water or saliva were 

 added to one part of the material taken from the incisor or 

 molar teeth. Further examination of the material showed 

 that out of a large number which were very different in 

 length, all were of the same thickness. Some were curved, 

 some straight, lying irregularly and interlaced." Since, he 

 says, "I had seen minute living animalculae of the same shape 

 in water, I endeavoured most carefully to observe whether 



