KNUT MIKAELSEN 



than total dose given. The fragment frequencies were very similar at the 

 same dose rate in the two experiments, while there is no correlation between 

 fragments and total doses given. 



This chronic radiation method is used to test certain chemicals for their 

 protective ability against radiation-induced chromosome aberrations. 



Table I. — Frequencies of chromosome aberrations in anaphase of meristematic root tissue o/Tradescantia 

 paludosa after exposures to chronic gamma radiation from ^"Co 



Protective property of certain chemicals on chromosomes is reported by 

 MiKAELSEN"*' ^' ^ Riley', Forssberg and Nybom^ Wollf^ and DevikI". 

 The results from my experiments are summarized in Table II, where gluta- 

 thione, cysteine, thiourea, sodium hyposulphite (NagSgOi) and sodium 

 cyanide (NaCN) proved to have protective property. 



Table II. — Per cent reduction in fragment frequencies at different concentrations of the chemicals tested 



The chemicals were applied in the following manner. To the nutrient 

 solution in which the Tradescantia cuttings were grown, the chemical com- 

 pounds were added at certain concentrations. After one hour's preabsorp- 

 tion, the plants, still in these solutions, were exposed to chronic gamma 

 radiation for 48 hours at a dose rate of 25 r/day which yielded a convenient 



317 



