C. DOBELL 329 



that this was not the case. Absolute proof of the matter could only 

 have been obtained, of course, by isolating a single individual from 

 the original culture and cultivating it further — a course which Massini 

 could not follow owing to the great technical difficulties involved. The 

 assumption that the original culture was pure was, however, rendered 

 extremely probable. The organisms, when grown in media containing 

 lactose (1 °/J, always produced red daughter-colonies, but they never 

 behaved in this way when grown in other media containing dextrose, 

 mannite, or other similar substances instead. 



Further cultivation of the colonies yielded remarkable results. The 

 organisms in the red nodules had permanently acquired the power of 

 fermenting lactose. They always produced red colonies on Endo's 

 medium — never whiter Even after transplantation on to other media 

 free from lactose, they never lost this power. Subsequent colonies 

 again grown on Endo's medium were invaiiably pure red. The 

 typhosii3-\ike original, therefore, had given rise to a number of new 

 individuals which closely resembled coli, having acquired the power 

 of fermenting lactose. 



Now the white parts of the colonies containing the red nodules 

 behaved exactly like the original organisms. When transplanted, 

 they produced colonies at first white but subsequently developing 

 red nodules, the individuals in which bred true. White colonies, if 

 transplanted every 24 hours, remained white : but they always pro- 

 duced red nodules if left for several days. The "white" race was 

 therefore to all appearances constantly undergoing a partial mutation 

 into a pure " red " race. Or, to put it in another way, the original 

 non- lactose- fermenting race constantly split up into two daughter 

 races — a pure lactose-fermenting race and a non-lactose-fermenting 

 race of the same nature as itself (i.e. with the power of splitting 

 into these two components again). The non-lactose-fermenting race 

 might therefore be called an " ever-sporting variety," and it was called 

 by Massini, in consequence, Bacterium coli mutabile. He regarded it 

 as a typhosus-Vike organism which was constantly undergoing mutations 

 into coli races'. 



The other characters of his remarkable race were carefully studied 

 by Massini. He also tried to discover whether other coli-typhosus 



1 In one instance, under peculiar conditions, a single white colony was obtained from 

 a red race. The red colonies never developed nodules. 



' Massini regarded the "red" races as typical races of B. coli. See however the 

 observations of Thaysen recorded on p. 333, footnote (infra). 



Jonm. of Gen. a 23 



