PART FIRST. 



I. 



HISTORICAL. 



IT is probable that Leeuwenhoeck, " the father of microscopy/' 

 observed some of the larger species of bacteria in faeces, putrid in- 

 fusions, etc., which he examined with his magnifying glasses (1675), 

 but it was nearly a century later before an attempt was made to de- 

 fine the characters of these minute organisms and to classify them 

 (0. F. Muller, 1773). 



In the absence of any reliable methods for obtaining pure cultures, 

 it is not surprising that the earlier botanists, in their efforts to classify 

 microorganisms, fell into serious errors, one of which was to include 

 under the name of infusoria various motile bacteria. These are now 

 generally recognized as vegetable organisms, while the Infusoria are 

 unicellular animal organisms. 



Ehrenberg (1838), under the general name of Vibrioniens, de- 

 scribes four genera of filamentous bacteria, as follows : 



1. Bacterium filaments linear and inflexible ; three species. 



2. Vibrio filaments linear, snake-like, flexible ; nine species. 



3. Spirillum filaments spiral, inflexible ; three species. 



4. Spirochcete filaments spiral, flexible ; one species. 



These vibrioniens were described by Ehrenberg as " filiform ani- 

 mals, distinctly or apparently polygastric, naked, without external 

 organs, with the body uniform and united in chains or in filiform 

 series as a result of incomplete division/' 



Dujajdin (1841) also placed the vibrioniens of Ehrenberg among 

 the infusoria, describing them as " filiform animals, extremely slen- 

 der, without appreciable organization, and without visible locomotive 

 organs." 



Charles Robin (1853) suggested the relationship of Ehrenberg's 

 vibrioniens with the genus Leptothrix, which belongs to the algae ; 

 and Davaine (1859) insisted that the vibrioniens are vegetable organ- 



