204 ALEXANDER HOLLAENDER 



with B. P. Kaiifmann (Kaiifmann et al.. 1946) on Drosophila and later 

 on with C. P. Swanson (Swanson and HoUaender, 194(3) on T radescantia 

 chromosomes, these stndies estabUshed ({uite well the synergistic effect 

 of near infra-red radiation. Some investigators now believe that the 

 canse is really in the far I'ed, not the infra-red. Incidentally, this red 

 effect will increase the X-ray damage signihcantly. The results of the 

 red effect are similar to that of the u.v. and X-ray combination. This 

 shows again that what we usually observe in oiu* measurements is 

 probably only a very small part of the action of ionizing radiation. 

 Through ignorance or failure to use more sophisticated methods of 

 radiation, we may miss some of the important initial effects of radiation. 

 The more we investigate details, the more it appears that there is hidden 

 from us a good j^art of the initial damage which the cells probably 

 repair themselves and which we have not been able to evaluate in any 

 quantitative manner. 



Another series of experiments is concerned with protection against 

 radiation damage by chemicals (Stapleton, 1960) and possibly some 

 different approaches to the repair of radiation damage after exposure 

 to radiation. The first of these projects is one in which I am especially 

 interested, that in regard to mutation production. We reported years 

 ago (HoUaender and Stapleton, 1955) that the mutation rate in .45^6/-- 

 gillus terreiis has always been inversely proportional to the survival of 

 the organisms that have been exposed to X-rays. In a careful analysis 

 of the survival curves, we learned that the killing curve in A. terreus 

 is S-shaped where up to 10,000 r no organisms are killed. It has also 

 been observed that one can protect against mutation jDroduction by 

 either the removal of oxygen or by using certain types of chemicals. 

 For all purposes, cysteamine was the most useful and most successful 

 one. But even after this treatment, the more cells that survive, the 

 lower the mutation rate. Inasmuch as we have no killing in .4. terreus 

 at doses below 10,000 r we thought we could investigate mutation rate 

 free of the complication introduced by decreasing survival. We pro- 

 ceeded by simi)ly plating a veiy few spores since the mutations are 

 usually crowded out and grow more slowly than the normal colonies. 

 We used between 20 and 50 plates, and thus only had a few colonies 

 on each plate. By this method we found (HoUaender and McCarthy, 

 1959) that the mutation rate is directly proportional to the amount of 

 radiation given and independent of the survival in the initial phase 

 where it is 100 per cent. If we give cysteamine in the proper concen- 

 tration during irradiation, the mutation rate is cut down significantly. 

 From these results, we infer that killing of cells and nnitation are not 

 necessarily interdependent and that we can ])rotect against mutation 



