234 C. p. RHOADS 



to injurious agents. Antibacterial substances such as gentian violet and 

 penicillin have been shown to cause the production of small resistant 

 colony variants of staphylococci (75). Many species of bacteria have 

 been exposed during their growth to immune sera with resultant 

 changes in their antigenic (chemical) structure (76). These experi- 

 ments must indicate, as discussed previously, that some factor which 

 controls the self -reproducing character of bacteria, analogous to genes 

 in the case of Neurospora, is changed as an effect of antisera, prepared 

 not against the genes themselves, but against the material which they 

 produce. It would be fascinating to know in what way, if any, the 

 further sensitivity of bacteria to agents such as ultraviolet light at 

 2650 A, a wave length known to injure specifically the genes of sexual 

 forms, is altered when a discontinuous variation due to the same agent 

 has occurred. Evidence is becoming available that resistance to ultra- 

 violet does follow exposure to it. 



Whereas the evidence indicates that each bacterial organism has an 

 inherent potentiality for producing a variant form once in a given 

 number of divisions, it is difficult, as with tissue cells, to analyze these 

 phenomena in the terms of classical genetics. To do so would of course 

 require the ability to see and to describe alterations of structures in the 

 vegetative cell which could be interpreted as having a function like the 

 chromosomes and genes of sexual forms. 



The studies of Lea (33) and of Gowen (34), mentioned previously, 

 bear on this point. From this work it is clear that the use of a physical 

 agent, x-rays, causes inherited alterations in viruses and bacteria similar 

 to the ones caused in the more complicated types of higher organisms. 

 In sexual forms the changes are known to be due to alterations of the 

 genes. In both sexual and vegetative cells the changes are believed to 

 follow hits on certain sensitive areas of the affected organism, areas 

 which appear to be functionally quite analogous to the genes. 



The transmutation of pneumococcal types, although it has been dis- 

 cussed repeatedly, deserves mention here. It can be depicted by a simple 

 formula: Avirulent, unencapsulated Type II plus killed Type III equals 

 virulent, capsulated Type III. 



The reaction requires for transformation a competent culture. This 

 culture may vary and result in non-encapsulated variants incapable of 

 reacting to the transforming substance. It is clear that there exist a 

 number of forms of unencapsulated variant pneumococci endowed with 

 varying potentialities and physiological abilities. The study is best 

 summarized by a direct quotation from Dubos (73a) : 



