460 RADIATION BIOLOGY 



effects must remain on a superficial level until the outlines of the more 

 underlying developmental reactions have been brought to light. In our 

 ignorance of the latter, most present attempts along these lines are neces- 

 sarily exploratory in character and their results must long remain 

 disconnected. 



Developmental reactions are of course physiological, in the broader and 

 at the same time more accurate meaning of that term. Moreover, the 

 recognized physiological processes of the adult are resultants of develop- 

 mental ones which preceded them, and some of which are still necessary 

 for their maintenance, or for their gradual change in the course of aging. 

 Thus the activities with which the physiologist deals are as much depend- 

 ent, in the end, upon genes and their interactions as are those studied by 

 the embryologist, and they are similarly susceptible to analysis through 

 the intensive investigation of the processes in question in individuals 

 having given mutant genes, and the comparison of these results with the 

 corresponding ones obtained in normal or other genetically contrasting 

 individuals. Illustrations of some well-known studies of this kind in 

 man are to be found in the investigations of myasthenia gravis, hemo- 

 philia, and pancreatic fibrosis. Such work helps to elucidate not merely 

 the pathological processes themselves but, as the other side of the medal, 

 the normal mechanisms which are in these cases deranged. Although 

 these hereditary conditions in man arose, of course, by spontaneous 

 mutation, it is to be expected that, in laboratory organisms, the induc- 

 tion of such changes by radiation will play an increasing role here just as 

 in the more strictly "developmental" studies. In fact, in one field of 

 pathology, the study of tumors, radiation has already been found useful 

 for obtaining, in Drosophila, genes giving rise to varied kinds of tumorous 

 growths, which have provided material for the study of the development 

 of such structures under different conditions. 



Underlying and participating in all developmental and physiological 

 processes, as well as all pathological ones, are biochemical reactions, and 

 it is of course these which constitute the most fundamental field of opera- 

 tions for the investigation of the more proximate effects of genes — those 

 effects on which and out of which all phenomena dealt mth by the 

 biologist proper and by the medical man are built. In other words, 

 whether a given activity of an organism is called biochemical or not 

 merely depends on the kind of equipment by which and the level of 

 analysis on which it is being regarded. To quote an earlier statement by 

 the present writer (1933): 



, . . each gene must be considered as producing its own specific chemical 

 material in the cell, as distinctive in its composition as insulin or thyroxin are, 

 . . . even though most of these materials do not circulate through the blood as 

 hormones, and have not been extracted, but remain within the cells in which they 

 are produced by the activities of the genes. It is a task for the future to deter- 



