20 THE BACTERIA. 



ganisms and especially to the bacteria. Their 

 origin, their evolution, the physiological peculi- 

 arities of their nutrition and reproduction, are 

 the object of numerous labors, and give rise to 

 passionate discussions relating to the subject of 

 spontaneous generation, polymorphism of fungi, 

 theories of fermentation, and the pathology of 

 virulent and infectious maladies. For this reason 

 an exposition of these researches, often contradic- 

 tory, is extremely difficult. We will make it suc- 

 cinctly, insisting especially upon the labors relating 

 to the classification of the bacteria, and reserving 

 to ourselves the privilege of returning to the his- 

 tory of several points, when we approach their 

 study in the special chapters of this thesis. 



The first important memoir published after 

 that of M. Davaine upon the bacteria is that of 

 M. Hoffmann, in 1869. He demonstrates : First, 

 that the bacteria are plants, having a very distinct 

 cellular organization ; second, that they can only 

 be classified in accordance with their form and 

 size, at first into monads and linear bacteria, and 

 the latter into microbacteria, mesobacteria, and 

 megabacteria ; (M. Hoffmann includes with the 

 linear bacteria, Vibrio, Bacterium, and Leptothrix, 

 which are bacteria united in a chapletj) third, 

 that mobility or immobility is not a specific char- 

 acter, but may present itself in the same species 

 under the influence of changes of temperature, of 

 density of medium, etc. M. Hoffmann shidies 

 also the origin of the bacteria, and rejects the 

 hypothesis of a spontaneous generation. As to 



