MAMMALIAN RADIATION GENETICS 149 



5 per cent 2 and 95 per cent He. No evidence for protection was noted. A similar 

 study with female mice did suggest some minor degree of protection. 1116 Mature 

 sperm may innately be hypoxic and thus no oxygen effect would be expected. 1140, 1142 



Kaplan and Lyon 686 tried the compound mercaptoethylamine which, like 

 hypoxia, is effective against general somatic damage. A 4 mg. dose given intra- 

 peritoneally about 5 minutes before exposure did not protect against dominant lethal 

 damage in males subject to 500 r of X rays. The same drug was used in a 10 mg. 

 dosage with rats exposed to 300 r of X rays. 839 Testicular weight loss was the end 

 point and no effect was noted. Eldjarn et al. 320 point out, however, that only very 

 small amounts of the drugs cysteamine or cystamine are localized in the testes (only 

 1 to 1 per cent of that observed in other organs) . The same may be true for the 

 compound used by both Kaplan and Maisin, which would suggest that considerably 

 larger dosages would be required. 



Rugh and Wolff 1086 succeeded in reducing damage to the ovary of the mouse with 

 a 3 mg. intraperitoneal dosage of either cysteamine or cystamine. The measures here 

 were the number of litters per mouse-week and the average number of fertile weeks. 

 Animals protected with cysteamine, for example, produced 0.084 litters per week as 

 compared to only 0.030 per week for controls after 50 r of whole-body X irradiation. 

 Protected females were fertile an average of 18 weeks, compared to 6 weeks for the 

 controls. Recently, Mandl 846, 847 has reported success with male and female rats 

 protected with B-mercaptoethylamine and cysteamine, respectively. She employed 

 a histologic measure of effectiveness : primordial-oocyte survival and spermatogonial- 

 cell survival. Intraperitoneal injections of 20 to 30 mg. were used, and a dose- 

 reduction factor of 1.5 to 3.0 was achieved over the dose range of 100 to 400 r. 



,No attempts have been made to study protection against specific mutational 

 damage. As Mandl has pointed out, the earlier failures may not have reflected an 

 inefficacy of the therapeutics but rather the wrong choice of dosage of both drug and 

 radiation, the former too low and the latter too high. Her success in increasing 

 survival of gonia and oocytes may encourage a more determined effort to search for an 

 agent that will reduce the yield of genie mutations. 



Selection of mammalian species and systemis) of mating. — To a degree, there is really 

 little room for choice when one wishes to carry out studies in mammalian radiation 

 genetics. The mouse has been and certainly will continue to be the favored species. 

 Some consideration, however, should be given the rat, at least for studies on growth 

 and maturation, since it may offer the opportunity to do more sensitive studies on these 

 traits. The unfortunate disadvantage for both mice and rats, and to some degree for 

 all litter-bearing animals, is the partialy uncontrollable incidence of neonatal mortality. 

 Since most litters are born during the early morning hours, the stillbirth and im- 

 mediate neonatal, or perinatal, mortality can be obscured by the cannibalistic ten- 

 dencies of the dams. In the writer's experience, it has sometimes been impossible to 

 determine the number born, although positive evidence of stillbirth, or livebirth, or 

 both, in the form of a few scraps of progeny partly eaten, may be available. An 



