VARIABILITY AMONG BACTERIA 25 



a little with the medium in which the organism is growing, and under 

 certain similar conditions the adhesion of bacteria to each other may also 

 vary. Thus cocci, which are ordinarily seen in short chains, may grow 

 in long chains. The capacity to form spores may be altered, and such 

 properties as the elaboration of certain ferments or of certain pigments 

 may be impaired. Also the characters of the growths on various media 

 may undergo variations. As has been remarked, variation as observed 

 consists largely in a tendency in a bacterium to lose properties ordinarily 

 possessed, and all attempts to transform one bacterium into an apparently 

 closely allied variety (such as the b. coli into the b. typhosus) have 

 failed. This of course does not preclude the possibility of one species 

 having been originally derived from another, or of both having descended 

 from a common ancestor, but we can say that only variations of an 

 unimportant order have been observed to take place, and here it must be 

 remembered that in many cases we can have forty-eight or more 

 generations under observation within twenty-four hours. 



