HISTORICAL. | 
their ré/e in the phenomena of the decomposition 
of organic bodies and in fermentations, M. Hoff- 
mann confesses “ that, with the exception of yeast 
and of the acetic and butyric ferments, all the rest 
is still enveloped 1 in obscurity.” . 
M. Cohn is the naturalist who, in our days, has 
occupied himself the most with the bacteria. In 
1853, he published his first researches upon this 
subject. The genera Zooglea, which he estab- 
lished at this time for the bacteria arranged in ge- 
latinous masses, diffused or more or less crowded 
together, was not a happy creation. It was adopt- 
ed at first by M. Rabenhorst who, in his work on 
the fresh-water algze of Europe, places them after 
the palmellaceze, while he classes the other bac- 
teria, Vibrio and Spirillum, in the family of the 
oscillatorie. The Zooglea are later abandoned by 
their author as a generic group, and are preserved 
only as the name of one of the diverse transitory 
stages through which the bacteria pass in the 
course of their evolution (Zooglea, Leptothrix, 
Torula). 
Twenty years later the same savant commenced 
the publication of a series of “ Memoirs”? upon 
these organisms (in his “ Beitrage zur Biologie der 
Pflanzen”’). In the first paper the author gives an 
exposition of his researches upon the organization, 
development, and classification of the bacteria, and 
upon their action as ferments. 
M. Cohn considers them as a well-defined group, 
— the schizospores, belonging to the alg, at the 
commencement of the series of the phycochroma- 
