320 KAN-ICHIRO MORISHIMA 



number of generations be subjected to an environment in which 

 this characteristic could again become useful. 



The inoculation of soUd media proved that all of our strains 

 of Bad. typhosum utilize both arabinose and dulcitol for their 

 nutrition. In fluid medium nearly half of the strains produced 

 acid in dulcitol in from five to twenty days while only a small 

 percentage showed acid production from arabinose. In striking 

 contrast to the behavior of the typhoid strains in xylose broth, 

 the strains that produced acid in arabinose or dulcitol in one 

 test often failed to produce acid when the test was repeated under 

 similar conditions. 



All of our typhoid strains gave rise to daughter colonies on 

 rhamnose agar, but none were observed to produce acid in 

 rhamnose broth. 



Our cultures showed no daughter colonies on raffinose agar 

 and did not produce acid in rafRnose broth. It is thus apparent 

 that instead of stating that a given species of bacterium ferments 

 such and such sugars, it should be said; that the organism in 

 question can utilize such and such sugars as a food; that the 

 organism produces acid in twenty-four hours in certain of these 

 sugars; that a majority of the strains produce acid after several 

 days in such and such sugars; etc., etc. Having obtained this 

 information concerning certain related species of bacteria it 

 should usually be easy to select those sugars which would yield 

 the most reliable information for the differentiation of the species. 

 Thus, Krumwiede (1918), and quite recently Jordan also, have 

 recommended acid production in rhamnose broth as the most 

 fundamental method of differentiating the paratyphoids from 

 Bad. typhosum. We agree that this is a good practical medium 

 for the differentiation of these species but we should bear in 

 mind that Bad. typhosum, although it does not show acid pro- 

 duction in rhamnose broth, is nevertheless able to utihze this 

 sugar as a food. 



Considerable discussion has arisen concerning the question 

 whether certain of the variations from the normal type mentioned 

 in this paper represent true mutations in the sense of de Vries. 

 The writer beheves that this term, which defined changes of a 



