NATURE OF THE GENETIC EFFECTS 445 



onts. There is vast room for the further development of valuable or 

 potentially valuable microorganisms for the production of foods, food 

 accessories, and pharmaceuticals (e.g., cheeses, wines, antibiotics), and 

 as food or fodder in themselves (e.g., yeast, plankton, algae), and also 

 for use in \'aried biochemical reactions of economic importance in other 

 ways, as in the production of innumerable industrially serviceable organic 

 materials, and in the synthesis, by the efficient use of solar energy, of 

 energy-rich combustibles. When the stupendous accomplishments of 

 natural evolution are contemplated, and then the momentous changes 

 even in comparatively long-lived species achieved by the trial and error 

 methods of primitive man, possibilities like the above for microorganisms 

 appear by no means too exaggerated to be in significant measure realized, 

 even within the space of a few decades, by artificially accelerated and 

 rationally guided evolution. 



Although in such work other mutagens than radiation can be used, 

 experience to date has indicated radiation to be the most satisfactory 

 agent for this purpose, because of its convenience of application, its pene- 

 tration, and the ready control of its intensity and timing. 



24. IRRADIATION OF THE GENETIC MATERIAL AS A MEANS OF 

 BIOLOGICAL INVESTIGATION 



A primary purpose of the theoretician as distinguished from the bio- 

 logical engineer, in applying radiation to produce changes in the genetic 

 material, is not merely to find given mutants or even to plot the inci- 

 dence of the changes found, but to use his results as a means of investi- 

 gating the mechanism whereby radiation brings about these alterations. 

 Studies of this type will be discussed in Chap. 8. Other purposes of 

 using this method of experimentation — interrelated with the above but 

 primarily concerned with biological problems proper — are to throw light 

 on the behavior, properties, and constitution of the genetic material itself, 

 and to attack varied problems of evolution, development, physiology, 

 pathology, and biochemistry in which genetics plays a role. It is not 

 surprising that thus far genetics itself has been the subject which has 

 been furthest advanced by this mode of attack, but the repercussions of 

 these advances have been far reaching elsewhere. In fact, so successful 

 has this tool proved in such work that only a cursory survey can be 

 attempted here, indicating the general types of results thereby obtained 

 in these fields. 



24-1. Field of Chromosome Behavior and Properties. As one example 

 of the contributions of radiation experiments to genetics, it may be 

 pointed out that the whole mechanism whereby structural changes of 

 chromosomes occur, whether as a result of irradiation or otherwise, has 

 been worked out chiefly through the studies on their production by radi- 



