NEUTRON EFFECTS OX ANIMALS 55 



organisms resulted from their exposure to sublethal doses of neutrons. It 

 is possible, of course, that certain individual cells were affected, and the 

 fact was hidtlen by the subsequent development of large numbers of un- 

 irradiated organisms. However, no abnormal colonies were found on 

 plates made at the beginning of the development of subcultures, even when 

 several such plates were made before active growth began. 



On the other hand, changes in the total population of resting cultiu-es 

 exposed to very low energy neutrons seem to indicate that there may be a 

 specific sensitivity to these particles. Such a hypothesis might account 

 for the occasional stimulation found in even the more exact experiments, 

 since the radiation from the cyclotron contained neutrons of this type in 

 low concentration. If it is assumed that the organisms are extremely sensi- 

 tive to slow neutrons, it might be possible to account for the erratic finding 

 of stimulation on the grounds of varying concentrations of slow neutrons 

 in the total radiation at different times. 



Such an assumption has not been pro^•ed by these experiments. More 

 work, with larger volumes of wax, is required before conclusions can be 

 drawn. It appears certain, however, that fast neutrons, delivered in in- 

 tensities much less than that represented by the designation 1000 n in our 

 experiments, do not produce any observable effect on the over-all behavior 

 of the microorganisms studied. If such neutrons are slowed sufficiently 

 to bring the "n" reading produced by the neutrons to a higher level than 

 that produced by the total radiation from the cyclotron without the pres- 

 ence of wax, growth may possibly be stimulated. 



CONCLUSIONS 



E. coli and euglena are relatively resistant to neutron bombardment- 

 Confirmation of the observation that neutron intensities over 1000 n will 

 produce demonstrable bactericidal effects on E. coli was obtained; such 

 dosages were also found to affect euglena cultures in some way which 

 restricts their motility. Smaller dosages of high energy neutrons have 

 little or no observable effect on the culture as a whole. There is some 

 indication, which merits further study, that E. coli may have a specific 

 sensitivity to very low energy neutrons. 



REFERENCES 



(1) Spear, F. G., Brit. J. Radiul, 17, 348 (1944). 



(2) HoLLAEXDER, A., AXD Claus, W. D., Natl. Research Council Bull. Xo. 100 (1937). 



(3) Exxs, T., Terrill, H. M., axd Garner, J. ■NL, Jr., Chapter 3. 



(4) Myers, W. G., and H.\xsox, H. J., Science, 101, 357 (1945). 



