CHAPTER XL 



CLASSIFICATION OF BACTERIA. 



LEEUWENHOECK,* two hundred years ago, recog- 

 nised, and described, microscopic organisms in 

 putrid water and saliva, which probably correspond 

 with organisms, such as vibrios and leptothrix ot 

 modern times. During two centuries these minute 

 beings have afforded histologists a subject for 

 controversy and dispute. Existing as they do upon 

 the very borderland of the vegetable and animal 

 kingdoms, not only have they been transferred from 

 one to the other, but even the question has been 

 raised whether the smaller forms should be con- 

 sidered as living beings at all. 



In reviewing the history of the various classifica- 

 tions which have from time to time been proposed, 

 we shall see that the gradual improvements in the 

 means of studying such minute objects, the methods 

 of cultivating them artificially, and of studying their 

 chemistry and physiology, and the ever-increasing 

 revelations of the microscope, have resulted in 



* Leeuwenhoeck, O. Omnia (Lugd. Batav., 1722). 



