INTRODUCTION. 19 



greatest astonishment/' he writes, " I observed distrib- 

 uted everywhere through the material which I was 

 examining animalcules of the most microscopic size, 

 which moved themselves about very energetically." 

 The work of this observer is conspicuous for its purely 

 objective character and absence of speculation ; and his 

 descriptions and illustrations are done with remarka- 

 ble clearness and accuracy, considering the imperfect 

 optical instruments at his command. There is little 

 doubt that Leeuwenhoek really saw some of the larger 

 species of micro-organisms which we now recognize as 

 bacteria, probably spirilla. 



It was not until many years later, however, that any 

 attempt was made to define the characters of these 

 minute organisms and to classify them. The first to 

 make such an effort was Otto Friedrich Miiller, in 

 1786 ; but having no means of obtaining pure cultures 

 all the earlier botanists naturally fell into serious errors 

 in the classification of bacteria. Thus various motile 

 organisms, which are now known to be of vegetable 

 origin, were commonly included under the infusoria, 

 which are unicellular animal organisms. 



Ehrenberg, in 1838, thus describes under the gen- 

 eral name Vibrioniens four genera of filamentous bac- 

 teria : 



1. Bacterium filaments linear and inflexible. 



2. Vibrio filaments linear, sinuous, flexible. 



3. Spirillum filaments spiral, inflexible. y. 



4. Sperochcete filaments spiral, flexible. 

 Dujardin, in 1841, also placed the vibrioniens of 



Ehrenberg among the infusoria, describing them as 

 extremely slender, filiform animals without appreciable 

 organization and without visible locomotive organs. 



