INTRODUCTION. 15 



of particular importance, not only because of the careful, 

 objective nature of the description given for the bodies 

 seen by him, but also for the illustrations which accom- 

 pany 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 astonished, 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 marked by 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 for the 

 origin of many obscure diseases. So universal was 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 



