54 NEUTRON EFFECTS ON ANIAL\LS 



difficulty by making use of two control samples, and planting immediately 

 after Ixjmbardment in each case. Such a procedure might possibly show 

 up reactions which occurred during bombardment and were subsequently 

 masked by overgrowth of the unaffected cells before the transplant was 



made. 



In the experiment illustrated, trouble with the cyclotron upset the pro- 

 posed time schedule. Instead of being about three hours old when irradi- 

 ated, the "wax" sample was actually six hours old. While the initial 100 cc. 

 culture would still have been multiplying actively at this time, it appeared 

 that the small sample — possibly due to difference in surface-depth ratio — 

 had passed into the resting phase at a much lower level than would be 

 anticipated. It is interesting to note that the sample exposed first grew 

 logarithmically in the transplant from the very beginning, while the second 

 sample and its control required a lag period. The fact that the lag period 

 in both bombarded sample and control were of about the same duration 

 argues against the reality of the apparent stimulation of growth under these 

 conditions. The behavior during logarithmic growth seems to indicate a 

 shorter generation time for the sample bombarded during the early part 

 of the resting phase, but it must be borne in mind that much higher counts 

 were anticipated and dilutions made accordingly. The counts, therefore, 

 must be considered inaccurate. 



In general, it was considered to be fairly well demonstrated that neither 

 death nor stimulation resulted from exposure of E. coli to doses of neutrons 

 considerably less than those employed by Spear (1); indication of stimu- 

 lation with very slow neutrons, however, remains to be confirmed. 



DISCUSSION 



Neutron bombardment might be expected to kill organisms outright, 

 as indicated by the work of Spear (1), or the neutrons might possibly alter 

 the metabolism or morphology of the organisms in some way, as has been 

 shown to occur in the case of molds (4). In our experiments, the first type 

 of reaction would have been observed as a reduction in the initial viable 

 counts in the subcultures from bombarded samples. Such a decrease was 

 not found, and it is further noted that the actual number of viable organ- 

 isms in the seedings were such as would have been present in similar 

 amounts of culture taken from these same subcultures at the conclusion 

 of the growth period. That is to say, the samples appeared to contain 

 as many viable organisms as the medium was capable of supporting. 



The failure of neutron bombardment, in intensities less than 1000 n, to 

 alter the rate of growth or duration of the lag period constitutes strong 

 presumptive evidence that no profound alteration in the metabolism of the 



