C. DOBELL 331 



Burk. Whet) sub-cultures were made from them by isolating indi- 

 vidual organisms, precisely the same results were obtained. That is 

 to say, it was found that a single individual (belonging to either race) 

 which at the outset was unable to split lactose, produced in presence 

 of this substance offspring which were in part like itself and in part 

 able to split lactose. The only possible objection to Massini's results 

 was therefore removed. Single individuals from " white " colonies gave 

 rise to mutating races : single individuals from " red " colonies bred 

 true. Their properties were unaltered by passage through animals, by 

 changes of temperature, or by phenol and other drugs. 



A series of investigations parallel to those which have so far been 

 mentioned has been conducted by Reiner Muller (1909, 1911), whose 

 work appears to have been extremely thorough. Altogether he has 

 studied several hundred races of organisms of the coli-typhosus group, 

 especially as regards their powers of fermenting 18 different kinds of 

 carbohydrates. 



The most important outcome of Muller's work has been the 

 demonstration that all typical races of B. typhosus behave towards 

 rhamnose exawtly as Massini's B. coli mutabile behaves towards lactose. 

 That is to say, typical pure races of B. typhosus are unable to ferment 

 rhamnose. When grown in a medium containing this sugar, however, 

 the colonies develop daughter-colonies (nodules) consisting of indi- 

 viduals which have permanently acquired the power of splitting 

 rhamnose. He claims that this is the most typical cultui^al character 

 of the typhoid bacillus*. Mutations of this sort invariably occur, and 

 under no conditions do the rhamuose-splitting organisms lose their 

 power. Muller has confirmed these observations in the case of indi- 

 viduals isolated by Burri's method. A single non-rhamnose-splitting 

 individual gives rise in the presence of this substance to offspring which 

 are partly like itself and partly able to ferment rhamnose. 



In the case of certain paratyphoid organisms {paratyphosus B., 

 Schottmiiller) Muller has found that rhamnose and lactose do not 

 produce any corresponding change. But the organisms behave to- 

 wards raffinose exactly as mutabile behaves towards lactose, or typhosus 

 behaves towards rhamnose. In other words, paratyphosus B. grown 

 in raffinose-containing media produces daughter-colonies which can 

 ferment this sugar — though the mother-colony cannot do so. These 

 raffinose-fermenting organisms never revert to the non-raffinose- 

 fermenting t3rpe. 



I No less than 120 races of B. typhottu were sttidied. 



23—2 



