Chapter 5 



A STUDY OF POSSIBLE REACTIONS OF ^vIICROORGANISMS TO 

 SUBLETHAL BOMBARDMENT WITH NEUTRONS 



By ROBERT K. JENNINGS and JAMES M. GARNER, Jr. 



Bacteria and other microorganisms are far from simple in their structure 

 and metaboHsm. Nevertheless, they would appear to offer a certain 

 amount of freedom from confusing side effects, when the fundamental 

 action of neutrons on living matter is under consideration. When multi- 

 cellular organisms are subjected to neutron bombardment, secondary reac- 

 tions to altered balance among organs, groups of cells, or even enzyme 

 systems are likely to be encountered, and it may be very difficult to decide 

 whether a given phenomenon should be attributed to the bombardment 

 directly, or to injuries produced in another part of the body. 



It was known (1) that sufficient dosages of neutron bombardment would 

 exert a bactericidal influence on vegetative cells of Escherichia coli and on 

 the spores of Bacillus mesentericus. The intensity of the irradiation re- 

 cjuired to achieve these results, however, was over 1000 n units of fast 

 neutrons. Unfortunately, it was necessary, during the period of these 

 observations, to give priority to pressing practical problems, which limited 

 the availability of the cyclotron. For the most part, it was not feasible 

 to subject our cultures to more than about a fifth of the required dosage. 

 Accordingly, we have been limited to the consideration of possible effects 

 of sublethal exposures. 



As might be anticipated, the results obtained were largely negative, but 

 may be of some value in guiding the efforts of future investigators. 



MATERIALS AND METHODS 



Test Organisms. Escherichia coli were used in the majority of the 

 experiments, since they have little tendency to form clumps or chains, are 

 sufficiently motile to form aliquot samples readily, are eas}^ to handle, 

 and because they had already been used by other investigators in studies 

 on the effects of various types of irradiation. Preliminary tests, more- 

 over, seemed to indicate that a mitogenetic response, reminiscent of the 

 growth stimulation which Hollaender and Claus (2) found with sublethal 

 exposure to ultraviolet light, might result from exposure to relatively small 

 intensities of neutron bombardment. 



Euglena were also considered as possible test organisms. They were 

 found to be ill suited, however, primarily because they appeared to be 



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