920 BIOLOGICAL EFFECTS OF RADIATION 



contradictory nature. The result has been that a large number of 

 scientific workers have become prejudiced against the problem; and 

 the problem has not received the consideration which the work of a 

 man of Gurwatsch's integrity deserves. 



A comparative statistical evaluation of all experiments verifying 

 the effect and of those yielding negative results would obviously be 

 unfair because of the general disinclination to publish negative results, 

 in the feeling that these may be due to faulty technique. It has been 

 stated that some investigators reporting negative results have not 

 always followed closely the technique described by Gurwitsch. These 

 workers often believe they have "improved" upon the original technique, 

 but by so doing they may have disregarded various important details. 

 This, also, can be understood easily since Gurwitsch has not published 

 a clear-cut, detailed description of the methods he has found most 

 successful. If the methods are such that each laboratory must largely 

 develop its own procedure, Gurwitsch himself should direct attention 

 to this point, but this he has not done. 



The study of the problem of mitogenetic rays is from what has been 

 said above, integrally related to the study of the stimulative action 

 by small quantities of ultra-violet light acting on biological materials. 

 As may be seen from allusions in various papers in this survey, the 

 idea that ultra-violet radiation may stimulate growth activity is a 

 point which is not well established, and in the present state of the litera- 

 ture on the subject it does not seem permissible to be too definite in 

 the matter. This point is discussed here only in so far as it is directly 

 necessary in order to understand the problem of mitogenetic rays. 

 The demonstration of the stimulative action of ultra-violet light does 

 not necessarily presuppose the existence of mitogenetic rays; but the 

 existence of such a stimulative effect is necessary for the understanding 

 of the alleged effects of these rays. 



CHARACTERISTICS OF MITOGENETIC RADIATION 



Before going into the methods reported as successful in the detection 

 of mitogenetic rays, it may be well to give a few of their characteristics. 

 The majority of the investigators report that the mitogenetic rays are 



o 



ultra-violet rays of about X1900 to 2500 A (48) and that they are of 

 extremely low intensity, about 100 quanta/cm. -/sec. (224). They 

 are reported to be given up by meristematic tissues or cells in a state 

 of active growth, by biological materials in which certain chemical 

 reactions take place, and by many chemical reactions in vitro. 



The short ultra-violet region of the spectrum, in which these rays 

 have been included, is a difficult region to utilize experimentally. Most 

 materials will absorb highly these wave-lengths and even quartz can 

 be used only if it is of very high purity. In addition to this, there 



