Vol. L January, IQ26 No. I 



BIOLOGICAL BULLETIN 



MODIFICATION OF DEVELOPMENT ON THE BASIS 



OF DIFFERENTIAL SUSCEPTIBILITY 



TO RADIATION. 



II. ARBACIA AND VISIBLE LIGHT FOLLOWING SEXSITIZATION. 



MARIE A. HINRICHS, 



NATIONAL RESEARCH FELLOW, DEPT. OF PHYSIOLOGY, 

 THE UNIVERSITY OF CHICAGO. 



Previous experiments by Bovie and Barr, '24, and by Hinrichs, 

 '24, have clearly demonstrated that living organisms are differ- 

 entially susceptible to lethal doses of radiation as well as to lethal 

 doses of other physical and chemical agents (Child, '24). Those 

 regions of the body which are physiologically the most active, are 

 the first to die and disintegrate. There is a progressive antero- 

 posterior disintegration gradient, coincident in lower animals 

 and embryonic stages, with the main body axis. Disintegration 

 gradients, as demonstrated by the method of photolysis, are 

 essentially like those produced by other chemical and other 

 physical agents. 



With sublethal doses of radiation, as with sublethal doses of 

 other agents, it is possible to modify embryonic development 

 (Child, '246, and Hinrichs, '24, and '25, now in press). With the 

 proper intensity and duration of exposure, the developmental 

 rates of various parts of the embryo may be relatively altered. 

 Here again the development of those parts which are physio- 

 logically the most active, is most easily inhibited or entirely 

 suppressed when doses are used which produce a permanent 

 inhibition, and do not permit recovery or acclimation. On the 

 other hand, if the inhibitory effect is slight or transitory, these 

 same regions of high physiological activity will be the first to 

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