X-Ray Sensitivity 111 



the log phase, with a return to initial sensitivity in the maximum 

 stationary phase. We have also followed organisms grown in glucose, 

 removed samples at certain time intervals, and studied their sensitivity, 

 and they seemed to follow somewhat the same pattern, at least in the 

 early stages of the growth cycle. 



Parkes: Has this kind of experiment been done on other unicellular 

 organisms? I am thinking of mammalian sperm, for instance. 



Hollaender: Not as far as I know. Experiments on oxygen tension 

 have been done on a wide variety of organisms. Dr. Kimball in our 

 laboratory has tried Paramecium, but as far as I know it has not yet 

 been done on sperm. 



Sloviter: Can you grow these cultures in the presence of small 

 quantities of radiation and make them resistant to large doses later? 



Hollaender: There is no adaptation to radiation as far as we know. 

 However, mutations are produced, and you may get a mutation which 

 is much more resistant. The resistant strain which I discussed, B/r, was 

 obtained by Witkin, irradiating a large bacterial population with 

 ultraviolet; out of the few that survived, one was resistant. 



Loutit: I have been most impressed by Dr. HoUaender's contribution 

 this afternoon because protection against the generalized effects of 

 radiation is a subject in which at the moment we are all particularly 

 interested. I think Dr. Hollaender has admitted that he has taken 

 the easy path by utilizing bacteria as his biological tool. We, amongst 

 others, have taken the hard road with mice. We were impressed with 

 Dr. Leon Jacobson's contribution to the International Society of 

 Haematology last August, where he showed that it was possible to 

 protect mice, not by measures taken before the irradiation, such as the 

 administration of cysteine or glutathione, but by measures taken after 

 the irradiation, and in his case this was the introduction into the peri- 

 toneal cavities of mice of spleens from infant mice. He showed that 

 splenic grafting, as it were, gave the same degree of protection as 

 shielding the spleen with lead during the irradiation. We have in our 

 laboratory repeated this work of Jacobson's, only on a much smaller 

 scale, and qualitatively we have been able to confirm his results. He 

 was able to show with his strain of mouse, the CF^, that he could alter 

 the median lethal dose from 600 r to something of the order of 1000 r. 

 With our strain of mouse, the CBA, we have not had nearly such drama- 

 tic results. We know that the normal median lethal dose of the unpro- 

 tected mouse is of the order of 800-850 roentgens, and that at 950 

 roentgens we can get figures like this: in the control mouse no stu'vival 

 out of 5 mice; in the protected mouse something like 3 survivals out of 

 5. Those are very small figures, it is true, but they do confirm Jacobson's 

 thesis. We have not been able to get any significant protection at 

 higher figures than 950 roentgens. 



We have also attempted to get protection, not from mouse spleens, 

 but from spleens of other animals. We have tried the introduction of 

 spleens from infant rabbits and from infant guinea pigs, and we find that 

 the hetero-specific test is entirely negative, whereas the homo-specific 

 test did show some positivity. 



