NO. 2 EFFECT OF ULTRAVIOLET ON ALGAE^ — ^MEIER I3 



raising the radiotoxic spectral sensitivity value to .331. The mean of 

 these two values is .291, which gives a reasonable value of .300 on 

 the smooth curve. 



2483 A. The algae were killed by this ray on two plates, but not 

 on two others at 120 seconds' exposure, which would give a radio- 

 toxic spectral sensitivity value of .356, which seems too high when 

 plotted. At an exposure of 165 seconds and at higher exposures, the 

 algae were always killed by this ray. If 165 seconds' exposure were 

 considered as the threshold, the radiotoxic spectral sensitivity value 

 would become .239, which seems too low in comparison with the 

 intensity of the line. However, the mean of the two values seems 

 reasonable, and on the smooth curve the point becomes .305. 



2536 A. This ray proved lethal at an exposure of 40 seconds, which 

 gives a radiotoxic spectral sensitivity value of .340. There was no 

 lethal effect with the 20 seconds' exposure, but as the intensity of 

 the ray is very high, there possibly would have been lethal effect at 

 31 seconds, which gives a radiotoxic spectral sensitivity value of .439. 



2576 A. The lethal threshold for this wave length apparently lies 

 at 240 seconds, which gives a radiotoxic spectral sensitivity value of 

 .613. Lethal regions for this ray are perceived on one algal plate at 

 120 seconds' exposure, but not on five others; again on one plate at 

 180 seconds' exposure, but not on another at the same exposure ; and 

 there were no lethal regions on the three plates made at an exposure 

 of 210 seconds. It is only at 240 seconds' exposure and higher that 

 this lethal region appears with certainty. 



2602 A. If the exposure of 240 seconds is considered the lethal 

 threshold of this ray, the radiotoxic spectral sensitivity value becomes 

 1.563, which is unreasonably high. In the experiment with 3-fold 

 intensity the threshold is at 150 seconds, which gives a more reason- 

 able radiotoxic spectral sensitivity value of .654. 



2652 A. The lethal threshold for this ray on the algal plates was 

 40 seconds, which gives a radiotoxic spectral sensitivity value of .372. 

 Considering the high intensity of this ray, a very large divisor (6.7) 

 was used to reduce it to the standard intensity of 1,000. Therefore 

 this point has small weight and is probably too low. It is possible 

 that lethal effect might have been produced at 30 seconds, since the 

 20 seconds' exposure showed no lethal effect. In that case the radio- 

 toxic spectral sensitivity value would be .495, and .650 on the smooth 

 curve. 



2699 A. 120 seconds' exposure to this ray produced lethal effects 

 in four dift'erent plates, giving a radiotoxic spectral sensitivity value 

 of .637, which is lowered to .625 on the smooth curve. 



