192 NUCLEOCYTOPLASMIC RELATIONS 



consistent with the hypothesis that the egg cytoplasm is a multi- 

 unit system, with one hit able to inactivate a unit and not all units 

 having to be hit in order to inactivate the system. This is an ex- 

 tension of Atwood and Norman's theory ( 1949 ) of multihit sur- 

 vival curves (see also Kimball, 1953). It is noteworthy that a 

 great deal of the cytoplasmic pentose nucleic acid appears to be 

 located in particles on the periphery. It should be pointed out that 

 a possible alternative explanation to that of unit inactivation by ul- 

 traviolet radiation is that of production of toxic substances. Wil- 

 bur, Bernheim, and their collaborators (see Bernheim et at, 1952; 

 Fisher and Wilbur, 1954 ) have described fatty acids oxidized by 

 ultraviolet radiation as being such substances. It would be inter- 

 esting to see if irradiated fatty acids can kill eggs and yield re- 

 sults identical to that of direct irradiation of the eggs. However, 

 since the action spectrum for killing indicates that nucleic acid or 

 nucleoprotein absorbs the energy, it appears more profitable at 

 present to explore the consequences of inactivation of cytoplas- 

 mic particles in the egg. 



The developmental events that follow irradiation of the cyto- 

 plasm suggest that normal synthesis is hampered. This, if true, is 

 of extreme importance. Overly fragile or badly constructed tis- 

 sues and disoriented tergites in surviving adults suggest a disloca- 

 tion of synthesis of structural proteins which may be the conse- 

 quence of inactivation of cytoplasmic pentose nucleic acid. The 

 work of Geigy ( 1932 ) on Drosophila indicated that fewer defects 

 in adults resulted when the egg was irradiated early than when 

 irradiated during differentiation processes. The tergite of the 

 adult is far removed both in time and space from the egg; since 

 the stages between them have not been worked out in Hahro- 

 bracon, any conclusions at present must be considered as tenta- 

 tive. 



When eggs were irradiated at shorter wavelengths, around 

 2300 A or less, it was found (Amy and von Borstel, unpublished) 

 that eggs killed by irradiating the cytoplasm have unusual char- 

 acteristics. They die at a much earlier stage of development and 

 the embryos have very little recognizable form. At these wave- 

 lengths, the proteins usually absorb more of the incident energy 



