INTRODUCTION. 15 



he discovered in the tartar scraped from between the 

 teeth a form of micro-organism upon which he laid 

 special stress. This observation he embodied in the 

 form of a contribution which was presented to the 

 Royal Society of London on September 14, 1683. This 

 paper is of particular 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. 



Upon seeing these bodies he was apparently very 

 much impressed, for he writes : " With the greatest 

 astonishment I observed that everywhere through the 

 material which I was examining were distributed animal- 

 cules 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 

 conspicuous absence of the speculative. His contribu- 

 tions 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 hardly 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 these u animal- 

 cules " and disease, that it amounted almost to a germ 



