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 Miller, 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. 
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. — 
