932 



BIOLOGICAL EFFECTS OF RADIATION 



unfair to generalize from these partial tests, especially when such work 

 as has been done with the spectrograph would apparently exclude any 

 possible chemical effects. Those who report favorably on mitogenetic 

 rays should evaluate critically not only the papers reporting "no effects" 

 but also papers which report "positive effects." In this way good 

 service would be rendered by the elimination of much material that 

 adds only to the confusion of this very difficult problem. 



It is known that the media (agar, etc.) in which yeast and bacteria 

 grow will absorb highly below X3000 A and that it will not transmit 



1 per cent of light below 

 ^ X2500 A, the presupposed 



upper wave-length limit of 

 mitogenetic rays. How is it 

 possible that an effect of the 

 order of magnitude of 100 

 quanta/cm. ^/sec. can be rec- 

 ognized in 1 to 2 cm. depth 

 in the detector suspension. 



f. 



> • * * ■ . • •■. 



:^ 



"W^ 



S^ 



QII 



I 



m 



n 



b 



(a) 



V 



(b) 



(c) 



Fig. 2. — Three arrangements for gastight isola- i o /-> -a. u 



tion of mitogenetic sources, (o) Incubator chamber f Or example .' Gurwitsch 



with quartz window (a/^er Baron)/ (b) chamber with nQg 122 127) explains this 



quartz window: I, quartz plate; II, tumor; III, '^ ' ' n i u j 



detector; IV, control; (c) chamber (a/<er5iac;ier):o, by the SO-Callcd Secondary 



quartz plate; h, radiating material; c, cement; d, radiation." In fact an 



stopper; e, detector;/, control. (GurmfscA, 108.) ,. ,, . ' ,. 



understanding oi mitogenetic 

 radiation is not now possible without an understanding of what is 

 here meant by secondary radiation. There are several explanations 

 suggested for this phenomenon, such as the following : (o) the incoming 

 radiation may activate an enzyme which will increase this small 

 stimulus and will finally produce a recognizable effect; (b) a chain 

 reaction may be set up since often only relatively small amounts of 

 energy are necessary to get a chain reaction started. This might 

 very well take place in the form of a modified explosion. Wolff 

 and Ras (309) have investigated secondary radiation more in detail. 

 They placed between the sender and detector a tube with quartz 

 windows 10 cm. long. This tube contained such as (a) dilute 

 bacterial suspensions, (6) suspensions from which the bacteria had 

 been removed by centrifugation, and (c) suspensions of nucleic acid. 

 The radiation leaving these intervening materials is, if the suspensions 

 are diluted enough, more intense than the radiation entering them, 

 although the materials cannot be used as secondary senders indefinitely. 

 However, they recover if not used for a certain period of time. In spite 

 of these explanations it is difficult to accept all these findings without 

 question. If they are correct, an entirely new field of investigation is 

 opened. But before accepting these findings, very much more quantita- 

 tive work must be done by way of confirmation and extension of present 



