470 JOHN W. G O W E N 



the effect of the selective destruction of given types of tissue or tissue 

 cells on immune reactions. Thus, the mouse of a particular genetic 

 strain may have its resistance lowered considerably if it is irradiated 

 with X rays. Such observations throw light on immune phenomena. 

 On the other hand, the experimental material is defective for the 

 study of the mechanism by which the X rays produce their effects, 

 for this mechanism ultimately goes dowTi into single cells, which 

 would be nearly impossible to isolate and study genetically. The 

 elucidation of such problems requires the types of studies involved in 

 such work as that on Drosophila. The same consideration holds for 

 the irradiation of tumor cells or cell tissues. The observations are 

 interesting from a physiological point of view, but for a critical under- 

 standing of what the X rays really do, are defective in that effects of 

 the X rays may be on a minute constituent of the cells, as, for in- 

 stance, the gene, which is in itself really responsible for the observed 

 physiological result. Similar considerations are important to the 

 study of the effects of radiation on either embryological development 

 or the regeneration of host tissues. 



Choice of the material for irradiation is of prime importance. By 

 preference this material should be well marked b}'^ genes so that the 

 effects of these genes on the embryological unfolding of the develop- 

 mental pattern could be studied. Experiments of this type have 

 led to interesting results in Drosophila, in which it has been possible 

 to time the separation of tissues, as those of the eye (22,46), from the 

 rest of the track. X-ray absorption is discrete even to particular 

 parts of the cell. This discreteness becomes quite evident in tissues 

 undergoing rapid and slow multiplication, the cells multipljang most 

 rapidly being those that express the effects of irradiation soonest. 

 Embryological and regenerative studies utilizing X rays may ma- 

 terially aid in the solution of problems of immune body production, 

 phagocytosis, hormone production, and other such vitally important 

 physiological phenomena. 



E. TYPES OF DATA ACCRUING FROM X IRRADIATION 

 OF BIOLOGICAL MATERIALS 



In the past, and, no doubt, in the immediate future, because of 

 the interest surrounding it, many of the observations on X-ray effects 

 on biological material have dealt with the survival of the given or- 

 ganisms under known doses of X rays and specified environmental 



