REDUCTION OF IRRADIATION EFFECT 



423 



100 



50- 



100 



50 





 100 



50 



38 irradiated non-exercised 



700 r 



26 irradiated exercised 



30 irradiated non-exercised 



26 irradiated exercised 



600 r 



10 



20 30 40 



Days post- irradiation 



50 



60 



Fig. 4. Effect of exhaustive swimming once a day on the survival of rats irradiated 



in the lethal range. [These data were lent by Dr. Kimeldorf and Dr. Fishier of the 



Naval Radiological Defense Laboratory, San Francisco; see (15).] 



Reduction of Irradiation Effect 



A vast store of information has accumulated on the mechanism of 

 ionization and the reactions of ionization products related to biological 

 effects of radiation. Two appHcations of this knowledge have given 

 promise of methods for reducing radiation effects, (a) Cysteine has 

 been shown by Patt et at. (18, 19, 20) to impart increased tolerance to 

 lethal levels of radiation if given just before irradiation. The effect is 

 roughly proportional to the quantity of cysteine administered when 50- 

 1500 milligrams per kilo body weight are administered 5 min before ir- 

 radiation. The response level of 50 per cent deaths (MLD^q) at 30 days 

 shifts from 725 to 1 100 r. Cysteine probably reacts with ionization prod- 

 ucts much more rapidly than other critical substances in the tissues 

 and thereby imparts a partial protection when it is present in signifi- 

 cant amounts. (6) Recognition has been made of the potentiality of 

 dissolved oxygen to be converted into toxic substances by the energy 



