INTRODUCTION 19 



the teeth a form of micro-organism upon which he laid 

 special stress. This observation he embodied in the form 

 of a contribution to the Royal Society of London on Sep- 

 tember 14, 1683. This paper is of peculiar importance, 

 not only because of the careful, objective nature of the 

 description given of the bodies seen by him, but also for 

 the illustrations which accompany it. From a perusal of 

 the text and an inspection of the plates there remains little 

 room for doubt that Leeuwenhoek saw with his primitive 

 lens the bodies now recognized as bacteria. 1 



Upon seeing these bodies he was apparently very much 

 impressed, for he writes: "With the greatest astonishment 

 I observed that everywhere throughout the material which 

 I was examining were distributed animalcules of the most 

 microscopic dimensions, which moved themselves about in 

 a remarkably energetic way." 



This discovery was shortly followed by others of an 

 equally important nature. His field of observation appears 

 to have increased rapidly, for after a time he speaks of bodies 

 of much smaller dimensions than those at first described by 

 him. 



Throughout all of Leeuwenhoek's work there is a con- 

 spicuous absence of the speculative. His contributions are 

 remarkable for their purely objective nature. 



After the presence of these organisms in water, in the 

 mouth, and in the intestinal evacuations was made known 

 to the world, it is not surprising that they were immediately 

 seized upon as the explanation of the origin of many obscure 

 diseases. So universal became the belief in a causal relation 

 between the " animalcules" and disease that it amounted 



1 See Arcana Naturae detecta ab ANTONIO VAN LEEUWENHOEK; Delphia 

 Batavorum, 1695. 



