CONGDON : EFFECTS OF RADIUM ON LIVING SUBSTANCE. — I. 353 



observations that the slow secondary radiations can injure tissue. 

 A comparison of the effect of rapid and slow radiations whose relative 

 energy values are known, has not to the Avriter's knowledge been 

 previously made. 



TABLE IV. 



Results of treatment with secondary rays from ganima rays, produced by 

 screening with a sheet of lead 4.5 cms. thick, 200 mgs. of 1/1000 strength of 

 pure RBr phis 10 mgs. of pure RBr. 



1 25% acceleration 



2 8% 



3 33% 



Average 22% 



In Table IV a source of radiation several times as intense as in 

 preceding trials was screened with four and a half centimeters of 

 lead to the exclusion of all direct alpha and beta particles. Secondary 

 beta radiations in small amounts were produced fi'om the lead by the 

 penetrating gamma rays which passed through it. Acceleration 

 resulted in each of the three experiments here reported. The trial 

 was made as a test of gamma radiation. The stimulating power of 

 even very weak secondary radiations shown by the preA ious experi- 

 ments indicates that the acceleration here also is, at least in part, 

 due to secondary electrons. 



Summary. 



The retarding effect on growth produced by beta radiations, from 

 100 mgs. of radium of one thousandth the strength of the pure bromide 

 in a cubical mass placed from one to two and one half centimeters 

 from Drosophila eggs for twenty-four hours, was more intense the 

 nearer the eggs were to the radium. At greater distances, up to five 

 centimeters, there was some evidence for slight acceleration. 



Secondary beta radiations (slow electrons) produced a much stronger 

 efPect than primary radiations (rapid electrons) of like-intensity. 



Tubularia. 



The exposures of Tubularia were varied not by changing the dis- 

 tance between the radimu and the pieces of hydroid, as in the case of 

 the Drosophila eggs, but by varying the period of exposure. Three 



