92 E. L. POWERS 



fates of the new chemical species must be governed by the same 

 physical laws. 



In order to apply the knowledge of the physical systems to the bio- 

 logical, one must design experiments to test parameters of the types 

 ntilized in ordinary jjhysical and chemical radiation experiments. It is 

 clear, however, that most functioning biological systems operate 

 successfully only within narrow environmental limits, and it is difficult 

 to apjily many physical experimental techniques to them. In conse- 

 quence there has been little progress in the understanding of early 

 events induced by high energy radiation in living systems. 



Very recent studies of two general kinds provide hope that descrip- 

 tions will be forthcoming of some of the early I'adiation-induced events 

 in cells that are important in bringing about biological effects. In 

 aqueous systems the use of very short pulses of radiation coupled with 

 fast, sensitive, detecting devices can circumvent the severe difficulties 

 one meets in analyzing a series of events that goes to completion in a 

 fraction of a second (see L. H. Gray in this Symposium). The other 

 general approach that promises early success is the use of dry biolog- 

 ical materials that can l)e exposed to a wide range of environmental 

 circumstances like those useful in physical experiments, and in which, 

 in addition, reactions are sufficiently slow to allow analysis with 

 ordinary techniques. Direct extension of the results obtained with this 

 kind of material to the wet biological system is difficult, because 

 water undoubtedly modulates the series of reactions. But the evi- 

 dence from the dry system aaIH provide a basis for asking many 

 questions, one of which is the difference made by the introduction of 

 water. 



The second approach is being pursued in several laboratories in which 

 a variety of biological materials such as plant seeds, pollen, dry bac- 

 terial cells and spores, and viruses are being investigated. 



In this lal)oratory we have been systematically investigating the 

 response of dry l)acterial spores to X-rays under a variety of environ- 

 mental circumstances. We have evidence for several of the early events, 

 and have been able to describe the characteristics of some of the pro- 

 ducts of irradiation and their relationship to radiation-induced damage. 

 In this paper we shall summarize briefly the evidence for several kinds 

 of identifiable chemical species, for the relationship of oxygen to them, 

 and the extent to which they participate in the biological damage 

 caused by X-rays. The results demonstrate the existence of the follow- 

 ing: an oxygen -independent portion (Class I) that can be sub-divided 

 into a radical s})ecies (lb) and one that may not be radical-like (la); an 

 oxygen-dependent portion that consists of very short-lived species 



