342 Mutation in Micro-Orgcimsms 



Baerthlein states, further, that by a similar procedure he is able 

 to make Staph, pyogenes aweus mutate into Staph, pyogenes albus^. 

 The albus race breeds true. But by treating it similarly, it will 

 "mutate back" into aureus races. Albus and aureus races are, 

 moreover, said to differ as regards the structure of the individual 

 organisms. 



Baerthlein records similar observations on a number of other 

 bacteria. But until further details of his work are available, it seems 

 useless to attempt to criticize his results or to correlate them with 

 those of Wolf and other workers in the same field. 



A case of an altogether different sort may now be mentioned. 

 Every bacteriologist is familiar with the fact that the power to form 

 spores is a very variable cliaracter in some races of bacteria. Sporo- 

 genic and asporogenic races have been observed in many different 

 species. In a recent paper, Eisenberg (1912) has given some inter- 

 esting facts concerning this matter in the case of anthrax bacilli. 

 His results are particularly noteworthy : for, although very many 

 similar observations have been made, the interpretation is not ex- 

 cluded that the results were due merely to a selection of certain pure 

 lines from an originally mixed population. 



Laboratory cultures of Bacillus anthracis may consist — according 

 to Eisenberg — of mixtures of sporogenic and asporogenic races (most 

 frequently), of pure asporogenic races (less often), or of pure sporogenic 

 races (seldom). Pure sporogenic and asporogenic races may be obtained 

 from a mixed culture ; the former by the action of heat, the latter by 

 constantly transplanting young cultui'es on to fresh media. A pure 

 sporogenic race may thus be obtained. And Eisenberg has found 

 that if it is constantly grown (5-20 transplantations) on glycerin-agar, 

 it completely loses its power of forming spores. These asporogenic 

 races bred true for a considerable time. They never reacquired the 

 power of forming spores. The conclusion appears to be justified, 

 therefore, that in B. anthracis a sporogenic i-ace may mutate into an 

 asporogenic race under certain conditions (in the present case under 

 the influence of glycerin ?). 



In his ingenious experiments with bacteria. Barber (1907)= en- 

 deavoured to obtain asporogenic races by the isolation of individual 

 organisms. A culture of organisms isolated from the juice of the 

 sugar-cane {B. megatheriunt '.) was found to contain some individuals 



' Compare Wolf, p. 340 suyni. ^ Vide infra, p. 345. 



