ACTION OF VISIHI.K KAYS ON ARBACIA EGGS. 7 



of a sensitizer like eosin appears to act primarily at the surface, 

 as for example in membrane elevation in Asterias eggs (Lillie 

 and Hinrichs, '23). 1 This effect may later be transmitted to 

 adjacent regions (Hinrichs, '24, Henri, '12, Schleip, '23). 



3. The action of light is a differential one (Bovie, '24, Hinrichs, 

 '24, '25). This is evident from the fact that disintegration in 

 lethal doses of radiation in the two spectral regions tested, ultra- 

 violet and the blue-green region of the visible, follows an antero- 

 posterior gradient along the axis of the body of lower organisms 

 or embryos. 



4. On the basis of such differential susceptibility to radiation, 

 it has been possible to modify the development of eggs of Fundulus 

 by exposure to ultraviolet radiation (Hinrichs, '25, unpublished). 

 In the resulting embryos, those regions of the body which have 

 the highest rates of physiological activity are the first to be 

 modified. Accordingly forms appear in which the central nervous 

 system, the heart and circulatory system, or the developing tail 

 region are abnormal. Such effects may be produced by exposures 

 made during the first ten minutes after fertilization, indicating 

 that at this early stage physiological differences are already 

 present which determine differences in susceptibility, i.e., such 

 differences exist even before there is any morphological differ- 

 entiation visible. 



5. Modification of development in Arbacia eggs is likewise 

 dependent on such early differences in susceptibility. Child 

 ('i6a) has been able to produce developmental modifications with 

 chemicals, and the results with radiation (see Child, '246, foot- 

 note, p. 109) give further evidence, (i), of the non-specific nature 

 of such susceptibility differences, and (2), of the dependence of 

 these differences on quantitative differences along the physio- 

 logical axes. Obviously there can be nothing specific, for ex- 

 ample, in the inhibition of development of the oral lobe region by 

 two such widely different agents as KCN on the one hand, and 

 ultraviolet radiation, or visible radiation following sensitization 

 on the other. 



A region of the body which has a relatively high rate of physio- 



1 Loeb, '07, Shippen, '07, and Pereira, '25, have found that eosin stains only 

 dead cells. In other words, destruction of the surface film precedes cell cytolysis 

 and subsequent staining by eosin. 



