836 Mutation in Micro- Organisms 



from these nodules were found to breed true (i,e. as regards power of 

 fermenting lactose). Attempts to obtain blue colonies from the " red " 

 individuals almost always gave negative results. However, by passing 

 the organisms from the red nodules through mice and rabbits they 

 succeeded in obtaining a race like the original — one, that is, which 

 produced blue colonies with red nodules on Drigalski-Conradi agar\ 

 It seems, therefore, that the acquired power of fermenting lactose — 

 which usually breeds true — may, under certain conditions, be lost. 



Results somewhat like those of Bernhardt and Markoff, but different 

 from those of most other investigators, have been just recorded by 

 Baerthlein (1912). He has studied 13 different races of coli-typhosus 

 organisms from the guts of healthy and diseased persons. All these 

 races behave like Massini's B. coli mutahile ; producing blue colonies on 

 Drigalski-Conradi agar, colourless colonies on Endo agar, but shewing 

 subsequently the characteristic mutations in the form of red nodules. 

 These lactose-splitting organisms were found to retain this character 

 after cultivation for a long time on Drigalski-Conradi and various 

 lactose-free media. Nevertheless, Baerthlein claims that if the lactose- 

 splitting organisms are cultivated continuously on ordinary agar, they 

 revert in part to the non-lactose-splitting form. After only 6-7 days 

 on agar, organisms transplanted back on to Drigalski-Conradi medium 

 develop into both red and blue colonies. It follows, therefore, that 

 after even so short an interval, the organisms may go back to their 

 original form. These observations do not seem to square with those 

 of most other workers. Perhaps the explanation is to be sought in the 

 fact that different observers have studied different races, which do not 

 all behave alike. Baerthlein, it may be noted, has supplemented his 

 work by a morphological, cultural, and serological study of his races*. 

 Confirmation of his results — by experiments on isolated individuals and 

 on related races — is much to be desired. 



1 The original "red" race was first tested and found to be pure. Bernhardt and Markoff 

 state that they succeeded "often" in performing this experiment, but "not always." With 

 the original strain of Massini, however, they obtained only negative results. 



2 From Baerthlein's paper it is to be gathered that the behaviour of B. coli mutahile 

 is even more complicated than at first appeared. He says that races of this organism 

 (and also of ordinary B. coli) undergo mutation when grown on ordinary agar. The 

 original race splits up into two constant daughter-races — (1) forming transparent colonies 

 consisting of long, slender, individuals ; (2) forming opaque yellowish colonies of shorter 

 and stouter individuals. Both these races when transplanted to a lactose-containing 

 medium mutate into a lactose-spUtting and a non-lactose-splitting race — though both 

 these retain the morphological characters of their originals. Four different races are 

 thus produced from the initial race. All may "revert" under suitable conditions. 



