INTRODUCTION 



When Roentgen made his great discovery in 

 1895 he could hardly have suspected the full 

 scope of its application. Only now, 50 years 

 after the discovery of X rays, can its signifi- 

 cance be appreciated. In examining only the 

 biological effect of these rays, which are mainly 

 stimulating and [new] form producing, the power 

 and significance of this new tool that has been 

 placed at the disposal of experimental science 

 must be marveled. 



A vast amount of experiments and observa- 

 tions has been performed over the past 50 years 

 demonstrating the effect of X rays on animal 

 and plant life. During this period the interest 

 shown in these rays by biologists has fluctuated. 

 Although the expectations of the first investi- 

 gators in the field of medicine have, in general, 

 been realized, a period of disillusion set in 

 before the successful use of these rays was con- 

 clusively established for the diagnosis and cure 

 of numerous diseases. 



Similar variations in attitude can be noted in 

 the evaluation of the biological effects of X rays, 

 depending on the success or failure of the experi- 

 ments performed. 



Interest in the effects of short waves appeared 

 shortly after their discovery, but the peak of 

 interest was reached in 1927 when Muller made 

 his announcement concerning the multifold in- 

 crease in the number of mutations obtained by 

 the use of these rays on fruit flies. Our biolo- 

 gists responded quickly to Muller' s discovery. 

 It seemed that a method had been found which 

 made it possible to induce an outburst of muta- 

 tions in any kind of plant or animal life. Among 

 these many mutations it would be easy to select 

 those which would be useful to agriculture and 

 industry. By selecting certain changes and by 

 fixing them by heredity, it was possible to ex- 

 pect to obtain new forms and even new species. 

 In short, X rays appeared to open wide horizons 

 for experimental production of new forms of life. 

 After a short while, however, assertions were 

 made on all sides to the effect that X rays had 

 not only failed to produce, but that they could 

 not produce the changes which the first investi- 

 gators expected. A few more years passed and 

 X rays assumed what we believed to be their 

 proper place in the field of biology. X rays are 

 not omnipotent; they have not produced new 

 families, or even new genera. But from the 

 changes produced by radiation it is possible to 



obtain not only radical deviations but forms 

 which are very desirable to the experimenters. 

 This will be demonstrated later by many ex- 

 amples. Certain publications in this area are 

 destined to become classics while others which 

 held great promise will be forgotten because 

 they were superficial or insufficiently checked. 



The same may be said in relation to phenom- 

 ena of stimulation due to exposure to X rays. 

 At first a great interest was taken in this type 

 of experiment. The majority of authors noted 

 that X rays had a positive effect on the rate 

 with which plants germinated and developed. 

 Then a series of works appeared denying that 

 X rays had any positive action. As a result a 

 sceptical attitude developed in relation to the 

 possibility of stimulating plant growth by the 

 irradiation of seeds or seedlings. Only in the 

 last few years have publications begun to appear 

 in the USSR as well as in the United States which 

 indicate that with appropriate dosages of these 

 rays it is possible to stimulate the growth and 

 development of agricultural crops and to in- 

 crease their yield. 



It is felt that this monograph should be 

 prefaced by a short explanation of the physics 

 of these rays. But first it is imperative to 

 comment upon the nomenclature of the rays. 



Roentgen called them X rays since he did not 

 clearly understand their properties. In due 

 time their name became so closely associated 

 with his that they quite properly received the 

 name of Roentgen rays. This is particularly 

 fortunate since it is most convenient for the 

 coining of such new terms as roentgenbiology, 

 roentgenmutation, ect. However, on certain 

 occasions we will resort to the term X ray for 

 brevity. 1 



The Physics of X Rays . In recent years 

 investigators have shown that atoms, which 

 were considered indivisible, are actually com- 

 plex structures consisting of a central nucleus 

 and an outer shell composed of the smallest 

 existing particles of matter, carrying negative 

 charges. These particles are called electrons. 

 In order to obtain X rays it is necessary to have 



H In this English translation, however, the term 

 X ray will be used exclusively.] 



