MODIFICATION OF DEVELOPMENT ON THE BASIS 



OF DIFFERENTIAL SUSCEPTIBILITY 



TO RADIATION. 



III. Arbacia GERM CELLS, AND (a) ULTRAVIOLET RADIATION, 

 (6) VISIBLE RADIATION FOLLOWING SENSITIZATION. 



MARIE A. HINRICHS, 



UNIVERSITY OF CHICAGO. 



Experiments made with x-rays, radium, ultraviolet radiation, 

 and visible light (following sensitization), 1 clearly demonstrate 

 that radiation may produce an injurious effect on living tissues 

 provided certain conditions are satisfied, namely; (a) the wave- 

 length range of radiation impinging on the tissue must include 

 that in which the tissue absorbs; (6) the spectral energy content 

 must be of sufficient magnitude, and (c) the duration of the 

 exposure must be long enough, to insure efficiency of action. 



When intensity and duration of exposure to a given radiation,. 

 e.g., ultraviolet radiation, are so regulated as to produce almost 

 immediate death, it is found that there is an antero-posterior 

 gradient of death and disintegration coincident (in lower animals 

 and early embryonic stages) with the main body axis. Those 

 regions of the body which are physiologically the most active 

 are the first to die and disintegrate. In other words, there is a 

 differential susceptibility to radiation in living organisms. (See 

 also Bovie and Barr, '24, Hinrichs, '24, and Child and Deviney, 

 '26.) 



On the other hand, a sublethal dose of radiation applied in 

 early embryonic stages, will differentially modify the later de- 

 velopment. Here again, the regions of high physiological activity 

 are first to be modified, and may be permanently inhibited, or if 

 the injurious action be only slight or transitory, these regions 

 may show recovery or acclimation more rapidly than other 

 regions. By regulating the dosage, differential inhibition or 

 differential acclimation (or recovery) may be obtained. 



1 See Clark, '22, Colwell and Russ, '24, Dubois, '14, Ellis and Wells, '25, Haus- 

 mann, '23, Hinrichs, '25, '26, L. Loeb, '22, for review of literature. 



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