998 RADIATION BIOLOGY 



some other species. One human case has recently been described in which 

 the equivalent of 390 r of soft X rays resulted in temporary epilation with 

 subsequent regrowth of normally pigmented hair (Hempelmann et al., 

 1952). The basis of graying, which is permanent once it occurs, is prob- 

 ably destruction of melanoblasts; graying in mice is the characteristic 

 effect of radiation on the inactive (nongrowing) stage, while active 

 follicles respond by epilation. It has been suggested (Chase, 1949) 

 that the increased melanoblast population of follicles in the active stage 

 acts to protect these follicles against loss of potentiality to produce 

 pigment. 



Eye. Superficial effects of irradiation on the cornea and conjunctiva 

 run parallel to effects on the skin, as regards dosage and the cyclical 

 nature of the response. It is of interest that a sensation of pain and 

 heat may be felt during irradiation with a few hundred roentgen equiv- 

 alents (Robbins et al., 1946). Many of the ocular lesions following total- 

 body irradiation are obviously the result of the systemic changes occur- 

 ring in the radiation syndrome (Wilder and Maynard, 1951). 



Lenticular cataracts are among the most serious nonfatal consequences 

 of irradiation. Although this has long been known, it received particular 

 emphasis in 1948 when several cases were discovered in physicists who 

 had been exposed to cyclotron neutrons (Abelson and Kruger, 1949) and 

 when survivors of atomic bomb irradiation began to develop cataracts 

 several years after the exposure (Cogan et al., 1949). The threshold for 

 clinically serious cataract formation by X rays in adult animals is prob- 

 ably close to the acute total-body LD 50 , but is relatively much lower 

 following exposure to neutrons, so that this effect is seen more often in 

 survivors of total-body neutron exposure. Young animals are more 

 susceptible than adults, and the latent period is related inversely to dose 

 (Leinf elder and Kerr, 1936). Intermittent dosage with fast neutrons 

 results in a particularly high ratio of effectiveness between neutrons and 

 7 rays where cataracts are used as the criterion (Evans, 1948) . The radia- 

 tion cataract is seen typically in the posterior capsular area, but a cyto- 

 logical analysis of the course of cataract formation shows that an impor- 

 tant component in its pathogenesis is the destruction of epithelial cells 

 that later migrate to this area (Cogan and Donaldson, 1951). 



Gonads. For a detailed account of radiation changes in the gonads the 

 reader is referred to Chap. 17 by Bloom and Bloom. The physiologic 

 responses resulting from irradiation of the testes and ovaries include 

 temporary or permanent sterility, certain endocrine responses, and, in 

 the case of the testis, evidence of impaired viability or diminished 

 numbers of sperm. 



Evidence of temporary sterility is first seen in the mouse about three 

 weeks after a single irradiation (Glucksmann, 1947). Examination of 

 the time course of survival of various cell types indicates that spermato- 



