228 C. P. RHOADS 



Blum (46) has reviewed the effects of ultraviolet light in great 

 detail. It is clear from his work that the wave length range responsible 

 for mutations and the absorption spectrum of nucleic acid in the ultra- 

 violet correlate closely with the effects of the light in causing cancer 

 (as well as erythema) of the skin in experimental animals. Here again 

 is evidence that a very specific agent, a narrow wave length range of 

 ultraviolet, clearly causative of mutations (or back mutations) in genet- 

 ically controlled material, is also active in inducing the change from the 

 normal to the neoplastic cell. 



The decreasing sensitivity to radiation shown by more differentiated 

 cells is striking and lends interest to any means by which the sensitivity 

 to mutation can be reduced. Swanson (47) has shown that if ultraviolet 

 is used followed by x-rays, the effects of the latter on chromosome 

 aberrations are partly suppressed. These findings suggest that the struc- 

 tures in the chromosome are not equally sensitive and that certain ones 

 are particularly susceptible to change induced by a specific physical 

 agent. This cannot be a rule, however, since a strain of Neurospora has 

 been reported with two different mutated genes, one the effect of x-rays 

 and the other of ultraviolet (48). 



Mutations Caused by Chemical Agents 



The induction of inherited changes, but not of cancer, by antisera 

 has been reported. Guyer and Smith (49) injected an antiserum to 

 rabbit lens protein into pregnant rabbits and reported that transmissible 

 ocular defects occurred in the offspring. Hyde (50) is stated to have 

 confirmed these observations. Lens protein is the product of a gene and 

 not a gene itself, but it may be that the modification of the product, an 

 antigen, modifies the gene in turn. It is also possible, as specified by 

 Sturtevant (50), that genes have chemical specificities corresponding 

 to the antigens which they produce, and so are affected directly by spe- 

 cific antibodies. The work of Emerson (51) tends to confirm this as- 

 sumption. He obtained from culture filtrates enzymes, described as 

 extracellular and adaptive in character, against which immune sera 

 were prepared and used to treat Neurospora. Resultant inherited 

 changes in the ability of the mold to produce the enzymes are reported. 

 It is possible that this principle provides an explanation of the results 

 of Kidd (52) and of Green (13) in injuring cancer cells by antisera 

 against them. 



For a very considerable period chemical agents other than antisera 



