ORGANIZATION OF THE BACTERIA. 31 



Color. The phenomena relating to the color 

 of bacteria have only recently been pointed out. 

 " But little attention has been given to the color 

 of the bacteria, regarded generally as colorless," 

 said M. de Seynes in 1874 ; and recently M. de 

 Lanessan, " The bacteria are ordinarily quite color- 

 less." However, M. Cohn had already insisted 

 upon the globular bacteria chromogenes, or of pig- 

 mentary fermentation, and upon the colors pro- 

 duced by different monads, which have long since 

 been studied by microscopists. 



Upon this subject, let us observe that the bac- 

 teria which are colored belong to two very dif- 

 ferent groups. First, colored organisms always 

 known as such, but which were not formerly in- 

 cluded with the bacteria, as the different monads, 

 which have become the Micrococcus prodigiosus, 

 cyaneus, aurantiacus,Cohn, etc. ; the second group 

 includes the bacteria properly so called, which 

 absorb the coloring matter of vegetables upon 

 which they are fixed as parasites, or of the media 

 in which they live. This is the case with the bac- 

 teria observed by M. de Seynes upon the Penicil- 

 lium glaucum, and perhaps with the Vibrio syn- 

 xanthus and sy?icyam^s,Ehrenb., which give to milk 

 a yellow or blue color according to the species. 

 We will return to this subject when we speak of 

 the nutrition of the bacteria. 



As to the purple-colored monads, they have 

 been especially studied as early as 1838 by Dunal, 

 then by Morren and Ehrenberg, and in our own 

 day by Kay-Lankester, Cohn, Klein, and finally 



