INTRODUCTION. 15 



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 with his primitive lens 

 had seen the bodies now recognized as bacteria. 



Upon seeing these bodies he was apparently very 

 much impressed, for he writes : " With the greatest 

 astonishment I saw that everywhere through the ma- 

 terial which I was examining were distributed animal- 

 cules of the most microscopic dimensions, which moved 

 themselves about in a remarkably energetic way." 



This observation 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 

 origi n of many obscure diseases. So universal became the 

 belief in a causal relation between these " animalcules" 

 and disease, that it amounted almost to a germ mania. 

 It became the fashion to suspect the presence of these 

 organisms in all forms and kinds of disease, simply 

 because they had been demonstrated in water. 



Though nothing of value at the time had been done 

 in the way of classification, and still less in separating 



