INTRODUCTION. 15 



In the year 1683 he discovered in the tartar scraped 

 from between the teeth a form of micro-organism upon 

 which he laid special stress. This observation he em- 

 bodied 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. 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 

 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 



1 See Arcana Naturae detecta ab ANTONIO VAN LEEUWENHOEK ; Delphis 

 Batavorum, 1695. 



