NEOPLASTIC ABNORMAL GROWTH 22/ 



the apparent absence of wave length effect in the x-ray range. Beadle 

 (25) states: "The curve of effectiveness of ultraviolet in producing 

 mutations against the wave length effect is sufficiently similar to the 

 absorption spectrum of nucleic acid over the same wave length as to sup- 

 port strongly the view that this substance is closely associated with genes 

 if not a component of them." The communications of Hollaender (41) 

 should be consulted on this point. This investigator points out that on 

 living cells the 2600 A region of ultraviolet is the most productive of 

 genetic effects. With Greenstein (42), he irradiated sodium thymonu- 

 cleate in water and observed that a decrease in streaming double bi- 

 refringence and viscosity occurred. A depolymerization was postulated. 

 Hollaender concluded that there was a primary absorption of the ultra- 

 violet by nucleic acid followed by the breakdown of the protein and the 

 disruption of the relation between the nucleic acid and the protein. 



It is important in this regard to consider the observations of Stanley 

 on variants of tobacco mosaic virus (43). Differences in the amount 

 of one or more amino acids, the presence of a new amino acid, and the 

 complete elimination of one amino acid were found. This indicates 

 again that, in variation, changes in protein composition may be quite as 

 important as effects confined solely to nucleic acid. Work of this type on 

 mammalian cells is urgently needed, and certain studies are in progress 

 under Brown in the Memorial Hospital laboratories. 



A particularly interesting observation, and one in keeping with Stan- 

 ley's results, is that of MacKenzie and Muller (44), who induced muta- 

 tions of Drosophila by wave lengths from 2800 to 3650 A. The effect 

 was especially marked at 3100 A, with a second maximum at 2280 A, 

 presumably a result of the absorption of energy by the protein com- 

 ponent. It would be interesting to explore this point further with other 

 types of organisms. 



Gray and Tatum (32) report failure in their efforts to cause varia- 

 tions analogous to mutations in sexual forms (Neurospora) in bacteria 

 by ultraviolet, but Beadle and Tatum (90) were successful in the case 

 of Neurospora, and rather more mutant strains were produced by ultra- 

 violet than by x-rays. Certain differences are reported between the effects 

 of the two agents. All but one of the mutations resulting in an inability 

 to synthesize thiamine were caused by x-rays and, in contrast, those in- 

 terfering with inositol and choline formation followed ultraviolet ex- 

 posure. This point is a particularly intriguing one since it suggests the 

 possibility that certain genes are more sensitive than others to one specific 

 physical agent. 



