QUANTUM THEORY OF RADIATION ABSORPTIONS IN TISSUES 1325 



enough for an exact quantitative comparison. The Drosophila survival 

 curve apparently requires r of our earHer formula to be 3 or 4. That is, 

 the most susceptible period is somewhat past the stage when the destruc- 

 tion of any nuclei is fatal. If the rates of death are compared it is found 

 that to have an equally sensitive volume to that of the egg would take 

 as a target something over a hundred sperm. The stage of development 

 of these eggs is unknown, but it seems unlikely that it is less than the 2^ 

 nuclei, or the stage when the chromatin volume of the egg would equal 

 that required for the sensitivity indicated. The maximum number of 

 nuclei at this stage would seem to be 2^^. The same line of reasoning 

 will account for the increase in susceptibility of the eggs with the tem- 

 perature at which they are previously developed. 



The foregoing discussion of the relative mortalities of the Drosophila 

 egg and sperm is presented only to show the manner in which well-known 

 biological factors might affect susceptibility to X-rays if the rays affected 

 the cell in the manner here discussed. There is one piece of evidence 

 which, unless the biological fact of decreased vitality through age or 

 some such variable accounts for the observed facts, would mitigate 

 against the theory of the direct effect of X-rays as due to random absorp- 

 tion in a relatively limited area of the chromatin. Hanson and Heys 

 (37) have shown that males which are irradiated wdth the same dose in 

 r-units and time at birth, 6, 12, 18, 24, and 32 days of age, show a pro- 

 gressively declining rate of mutation; 13.8, 11.3, 8.9, 5.8, 2.1, and 0.6 per 

 cent, respectively. No analysis of the reasons behind this decline in 

 observed mutation is presented. 



SUMMARY 



This paper discusses the biological aspects of the quantum theory 

 of radiation absorptions. The genetic results for X-ray treatments 

 show that the X-rays produce their effects on chromatin in minute 

 localized volumes. These volumes are of the order of 1 X 10~^^ cc. and 

 may number 2000 to 15,000 to the cell. 



REVIEW REFERENCES 



LoEB, L. Effects of Roentgen rays and radioactive substances on living cells and 



tissues. Jour. Cancer Res. 7: 229-282. 1922. 

 Oliver, C. P. Radiation genetics. Quart. Rev. Biol. 9: 381-408. 1934. 

 Packard, C. The biological effects of short radiations. Quart. Rev. Biol. 6 : 253- 



280. 1931. 

 Timof^eff-Ressovsky, N. W. Die bisherigen Ergebnisse der Strahlengenetik. 



Ergeb. Med. Strahlenforsch. 6: 129-228. 1931. 



REFERENCES 



1. Altenburg, E. The effect of ultraviolet radiation on mutation. Anat. Rec. 

 41:99. 1930. (Abstr.) 



