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 
(O. F. Miiller, 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 
microérganisms, 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 Infusorva are 
unicellular animal organisms. 
Ehrenberg (1838), under the general name of Vibrioniens, de- 
scribes four genera of filamentous bacteria, as follows : 
1. Bactertum—filaments linear and inflexible ; three species. 
2. Vtbrio—filaments linear, snake-like, flexible ; nine species. 
3. Spirillum—tfilaments spiral, inflexible ; three species. 
4, Spirocheete—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.” 
Dujardin (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 alge ; 
and Davaine (1859) insisted that the vibrioniens are vegetable organ- 
