330 Mutation in 3Iicro- Organisms 



organisms' behaved in a similar manner, but he could find no evidence 

 that this was so. It may be mentioned that as regards their virulence 

 and agglutination reactions the " white " and " red " races appeared to 

 be identical. 



It is somewhat remarkable that all the numerous workers who 

 have subsequently studied these organisms have confirmed Massini's 

 observations. But later workers have been able to amplify his work 

 in several directions, and have discovered similar phenomena in many 

 other races of coli-ti/phosus organisms. 



Twort (1907) recorded independently that certain coli-typhosus 

 organisms were able to acquire the power of fermenting certain 

 sugars if grown in them for a sufficiently long time. The change 

 took place slowly. In this manner he modified dysentery bacteria 

 (Kruse and Flexner strains) so that they were able to ferment saccha- 

 rose: and he was able to train B. typhosus to ferment lactose and dulcite. 

 The organism which had acquired the power of splitting dulcite is 

 stated to have retained this power permanentl}' — even after passage 

 through a guinea-pig and cultivation in a dulcite-free medium. 



Burk (1908) isolated an organism almost exactly like that studied 

 by Massini. He made similar observations upon it. Sauerbeck (1909) 

 records closely similar results. 



Beuecke (1909) and Kowalenko (1910) were able to confirm 

 Massini's results and to make an important addition to them. They 

 succeeded in isolating and testing individual organisms. Both ob- 

 servers adopted Burri's Indian ink method-, and obtained the same 

 results, which completely agreed with Massini's original results. As 

 Kowalenko's results are recorded in greater detail, they may be given 

 here, though Benecke's were recorded first. 



Kowalenko (1910) obtained both the races studied by Massini and 



' Amongst the forms investigated were typical B. coli, B. typhosus, Flexner bacilli, 

 Shiga bacilli, and paratyphosus races. 



2 The introduction of this ingenious method has made it possible to isolate and 

 cultivate individual organisms from a colony of bacteria with comparative ease. (See 

 Burri, Das Tuscheverfahren, Jena 1909.) In principle the method is as follows. 

 A drop of fluid containing a few bacteria is mixed with a sterile solution of Indian ink. 

 A minute drop of the mixture is then placed under a cover-glass and examined under the 

 microscope. The bacteria can be seen, under a comparatively low magnification, as 

 white dots in a black field : and the small number of individuals in each preparation 

 can be counted. Those preparations containing but a single individual are then selected, 

 their contents transferred to a suitable culture medium, and cultivated further. In this 

 way it may be known with certainty that the culture produced has sprung from one 

 original individual. 



