PROTECTION 199 



phonate intraperitoneally administered a few minutes before irradiation 

 (101). 



Rats are partially protected from radiation effects by intravenous ad- 

 ministration of cysteine (39, 39a, 113). Cysteine injected into the skin 

 of guinea pigs partially protects the hair follicle from radiation effects 

 (38). SH groups disappear in the skin of the guinea pig after irradiation 

 (109). Massive doses of glucose (20 g) have a similar effect on the hair 

 follicles of the rabbit (40). Hollaender (133) has shown that bacteria 

 previously grown in broth containing glucose are thereafter less radio- 

 sensitive than bacteria grown in ordinary broth. Latarjet (37) interprets 

 these results as due to the loss under irradiation of glucose of some 

 hydrogen which combines with the oxidizing agents to produce H2O2, 

 and thus prevents these agents from combining with the sensitive mole- 

 cules. Latarjet has in certain cases observed that an increase in H2O2 

 production was accompanied by a decrease in the biological effect of 

 irradiation. 



Cysteine may exert its protective action in different ways. In the 

 leaf of the zinc-deficient walnut tree cell division is stopped in the pro- 

 phase, quinone being formed in these leaves by oxidation of dihydroxy- 

 phenols. The mitotic index increases by addition of cysteine. The ef- 

 fect of cysteine has been ascribed by Reed (40a) to the fact that cysteine 

 contains the group R — SH, which can donate H, thereby enabling the 

 cells to keep the dihydroxyphenols in a reduced state, whereas they 

 would otherwise be oxidized to quinones by the polyphenoloxidase. 

 Normally, tissue would contain enough reducing substances to reduce 

 quinones back to dihydroxyphenol derivatives, but not, however, when 

 grown on a zinc-deficient soil. 



Besides the above-mentioned protecting effect of substances containing 

 — SH groups, other agencies affecting cellular oxidation may also pro- 

 duce a protective action. 



Intraperitoneal injection of 0.1 mg sodium cyanide immediately be- 

 fore irradiation was found to protect 50-80 per cent (41, 42, 43, 112, 125), 

 and injection of 0.1 mg sodium nitrite to protect 20 per cent, of irradiated 

 mice from the lethal effect of x-radiation. Only a small protective effect 

 was observed if the injection (which took 6-7 min) was given immedi- 

 ately after the irradiation, while all protective effect was absent if the 

 injection took place 15 min after irradiation. The protective effect was 

 observed only if the dose administered did not differ widely from the 

 lethal dose of about 700 r. If 900 r was given, only 20 per cent of the 

 mice were protected by NaCN injection, and protection was not demon- 

 strated if the dose was as high as 1200 r, or if a daily dose of 84 r was 

 given for 12 days. 



