INTRODUCTION 3 



ible at this time, but they were regarded by many 

 as evidences of an unbalanced mind, most writers at 

 that period doubting the possibility of the micro- 

 organisms being living things. In 1786 a Danish 

 zoologist, Miiller, described many structural details 

 of bacteria of which his predecessors were ignorant, 

 and also recognized the extreme difficulties of study- 

 ing such minute organisms. "The difficulties/ 7 he 

 writes, "that beset the investigators of these micro- 

 scopic animals are countless; the sure and definite 

 determination [of species] requires so much time, 

 so much acumen of eye and judgment, so much 

 perseverance and practice, that there is hardly 

 anything so difficult." (Jordan.) 



In 1838 Ehrenberg (1795-1876) made a valuable 

 contribution to the subject in his work on " Infu- 

 soria," as the organisms found in infusions of meat, 

 hay, and other substances were called. Ehrenberg 

 was the first to introduce a really systematic 

 method for the study of bacteria. 



It was not until Louis Pasteur (1822-1895), about 

 1850, began his investigations upon the souring and 

 putrefaction of beer and wine that bacteria were 

 recognized as organisms whose activities were of 

 such significance to the human race. 



For two hundred years prior to Pasteur's investi- 



