THE PROBLEM OF MUTATION 435 



on agar, and later he claims that by means of animal passage he 

 had transformed a number of viridans strains into pneumococcus, 

 and a number of hemolyticus strains into viridans. Similar claims 

 have Been made by Davis. 107 It is very difficult to comment upon 

 these results. Broadhurst 108 also observed changes in fermentation 

 reactions produced in streptococci when they were subjected to 

 growth in fresh milk, saliva and extracts of fresh tissues, but she 

 draws conservative conclusions, and changes such as those noted 

 by her, might well be minor ones in their biological significance. 

 The fundamental changes noted by Rosenow particularly would 

 serve to disturb considerably the methods of classification now em- 

 ployed. The subject is so important that the greatest conservatism 

 in critical evaluation of these claims must be exercised. There are 

 many sources of error, such as the possibility in animals of injecting 

 one organism and getting another one out, and the many possibilities 

 of contamination, that further work must be done along these lines 

 before judgment can be finally given. We, ourselves, have put 

 viridans organisms into rabbits in open celloidin agar capsules, by 

 a method described by Raymond and ourselves 109 and have, after 

 four months, recovered the identical unchanged organisms that we 

 put in, although they had been in the rabbit as long as four months. 

 It is our opinion at the present time that such fundamental muta- 

 tions do not take place, and that it will take a great deal of very 

 careful and accurate work before such claims can be seriously 

 considered. 



Davis, Jour. Infee. Dis., 12, 1913, 386. 



108 Broadhurst, Jour. Infec. Dis., 17, 1915, 277. 



109 Zinsser and Raymond, Transac. Soc. Exper. Med. and Biol., January, 1921. 



