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 writer’s knowledge been 
previously made. 
TABLE IV. 
Results of treatment with secondary rays from gamma rays, produced by 
screening with a sheet of lead 4.5 cms. thick, 200 mgs. of 1/1000 strength of 
pure RBr plus 10 mgs. of pure RBr. 
1 25% acceleration 
9 8 % 66 
3 33% i. 
Average 22% ef 
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 from 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 previous 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 
effect than primary radiations (rapid electrons) of like intensity. 
Tubularia. 
The exposures of Tubularia were varied not by changing the dis- 
tance between the radium and the pieces of hydroid, as in the case of 
the Drosophila eggs, but by varying the period of exposure. Three 
