INTRODUCTION. 



HISTORY. The microscope was invented about the latter 

 part of the sixteenth century ; and soon after, by its aid, 

 minute organisms were found in decomposing substances. 

 Kircher, in 1646, suggested that diseases might be due to 

 similar organisms ; but the means at his disposal were in- 

 sufficient to enable him to prove his theories. Anthony 

 Van Leuwenhoeck, of Delft, Holland (1680 to 1723), so 

 improved the instrument that he was enabled thereby to 

 discover micro-organisms in vegetable infusion, saliva, fecal 

 matter, and scrapings from the teeth. He distinguished 

 several varieties, showed them to have the power of loco- 

 motion, and compared them in size with various grains of 

 definite measurement. It was a great service that this 

 "Dutch naturalist" rendered the world; and he can rightly 

 be called the " father of microscopy." 



Yarious theories were then formulated by physicians to 

 connect the origin of different diseases with bacteria; but no 

 proofs of the connection could be obtained. Andry, in 1701, 

 called bacteria worms. MUller, of Copenhagen, in 1786, made 

 a classification composed of two main divisions monas and 

 vibrio ; and with the aid of the compound microscope was 

 better able to describe them. Ehrenberg, in 1833, with still 

 better instruments, divided bacteria into four orders: bac- 

 terium, vibrio, spirillum, and spirochaBte. It was not until 

 1863 that any positive advance was made in connecting 

 bacteria with disease. Rayer and Davaine had in 1850 



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