SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 95 



2323 A. This ray produced a lethal effect with an exposure of 480 

 seconds, which gives a radiotoxic sensitivity value of .943. This value 

 seems too high. In the 3-fold intensity experiment, 2323 A was lethal 

 with 300 seconds' exposure on one plate, but not on any other plate, 

 which would seem to indicate that the threshold is higher than 300 

 seconds. If an exposure time of 400 seconds is selected, a radiotoxic 

 spectral sensitivity value of .357 is obtained. 



2352 A. Algal cells were first killed by this ray at an exposure of 

 480 seconds, which gives a radiotoxic spectral sensitivity value of 

 .347 and a value of .404 on the smooth curve. 



Fig. I. — Radiotoxic spectral sensitivity of ChlorcUa vulgaris to ultraviolet rays. 

 The abscissae are wave lengths in angstroms. The ordinates are relative lethal 

 effectiveness in arbitrary units. Black line, smooth curve ; dash line, actual 

 values; dot line, curve obtained by Meier (1934). 



2378 A. There was lethal action by this ray with an exposure of 

 240 seconds, which gives a radiotoxic spectral sensitivity value of .442. 



2399 A. The lethal threshold of this ray is at 240 seconds' exposure, 

 thus giving a radiotoxic spectral sensitivity value of .417, 



2447 A. A lethal effect is first produced by this ray in the algal 

 plates exposed for 960 seconds. The radiotoxic spectral sensitivity 

 value is .326. 



2463 A. On the algal plates, lethal effect was observed with an 

 exposure of 960 seconds at two slightly different intensities, namely, 

 416 and 429 ergs/sec. cm^ The lethal factor for 960 seconds at 

 416 ergs/sec. cm"* is .251. The exposure lower than 960 seconds was 

 720 seconds, and although there was no lethal effect on the algae at 

 one 720-second exposure, it seems very possible, considering the in- 

 tensity of the line, that there might be lethality at 725 seconds, thereby 



