HISTORICAL. 21 



their role 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 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 Zoogloea, 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 algae of Europe, places them after 

 the palmellaceae, while he classes the other bac- 

 teria, Vibrio and Spirillum, in the family of the 

 oscillatoriae. The Zooglcea were 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 (Zooglcea, Leptothrix, 

 Toruld). 



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 algae, at the 

 commencement of the series of the phycochroma- 



