936 BIOLOGICAL EFFECTS OF RADIATION 



great enough to detect the intensity of radiation said to characterize the 

 mitogenetic sender. In spite of this, positive results are reported. 



Schreiber and Friedrich (252) pubUshed at about the same time as 

 Rajewsky an apparently thorough investigation with a modified counter, 

 the sensitivity of which is reported to be not so great as that of the one of 

 Rajewsky. They report entirely negative results. 



Seyfert (261), working in Geiger's laboratory, constructed the 

 Geiger counter as modified by Rajewsky, and he reports a sensitivity of 

 10 quanta/cm. Vsec; furthermore, in what appears to be a thorough 

 investigation he obtained entirely negative results. 



Lorentz (176) in this country reports work on the same type of counter 

 with a reported sensitivity of 10 quanta/cm. ^/sec. A number of mate- 

 rials which had been reported to be senders gave no effects on his counter. 

 Grey and Ouellet (90) using a high sensitivity counter report entirely 

 negative results with sea-urchin eggs as sender, in spite of the fact that 

 these have been reported to be unusually good emitters of mitogenetic 

 rays. 



It is very difficult to decide upon the question of the use of the 

 modified Geiger counter for the detection of mitogenetic rays, since both 

 positive and negative results have come from laboratories with well- 

 established reputations for good work. Further work must be awaited. 

 Especially is it important that a thorough statistical evaluation be made 

 of the work alleging positive results. Certainly it is necessary to find 

 out whether all precautions against temperature changes, spurious elec- 

 trical effects, adsorption phenomena, etc., have been taken. If we are to 

 work with an instrument of a sensitivity of 10 quanta/cm. ^/sec, cus- 

 tomary precautions are far from being sufficient. It is not clear to the 

 reviewer that the sensitivity of these counters, which have been deter- 

 mined by classical methods — methods which until now have been used 

 only when millions of quanta were available — will apply also when 10 to 

 100 quanta/cm. 2/sec. are at our disposal. A more detailed discussion of 

 this point will be given in another article. 



If we ignore the work where the results have been negative and 

 accept the modified Geiger counter as an established instrument, we are 

 apt to wonder why, during the four years that this instrument has been 

 reported to be used successfully, no actual new work with the counter as 

 detector has appeared. Only such work as has been reported to be 

 successful with the biological detectors has been checked with the Geiger 

 counter and this only in a relatively small number of cases. One of the 

 senders most frequently used— yeast — has never recorded radiation on 

 the counter. 



PHYSICAL PROPERTIES 



The physical properties of mitogenetic rays are said to be, so far as 

 studied, the same as those of any other ultra-violet radiation. The light 



