6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



as there still seemed to be some doubt as to the results of the red 

 and yellow filters, a third experiment was run repeating the red 

 and yellow, and with the duplicate infrared filters in place of the 

 green and blue ones. 



RESULTS 



CELL MULTIPLICATION 



The cells in five drops of each culture were counted and the mean 

 was determined. As determined by the microscopic count, there was 

 an average of seven cells in a drop of the initial cultures before 

 treatment. The ratio of the means of the final to the initial cell count 

 of each culture after 2 weeks of exposure to the different wave-length 

 regions is recorded in table 2. 



The nephelometric measurement, or the intensity of the light trans- 

 mitted by each culture, was determined before and after each experi- 

 ment. The ratio of the final to the initial measurement for each wave- 

 length region is likewise recorded in table 2. 



An examination of the cell count ratios and the nephelometric 

 measurement ratios in table 2 shows that the check culture varies less 

 from the treated culture of each region according to the nephelometric 

 measurements than it does according to the cell counts. The cell 

 counts of the check cultures show that darkness had a depressing 

 effect on the cell multiplication, whereas the nephelometric measure- 

 ments of the check cultures record the turbidity of the solution. 

 Consequently, it hardly seems that the nephelometric measurement 

 ratios should receive as much weight as the cell count ratios. A 

 comparison of the two types of measurement shows that the nephe- 

 lometric measurement results roughly support the cell count results. 



A correction to the nephelometric indications was thought to be 

 advisable, and was made as follows. It appeared that the nephelo- 

 metric values showed a small increase of turbidity for the liquids 

 which remained in darkness. (See table 2.) As counts showed that 

 such a change was not caused by multiplication of algae, it seemed 

 probably to be due to another cause, not readily ascertained, but no 

 doubt equally operative with the flasks in which the algae were treated 

 with radiation. Hence it seemed proper to divide the nephelometric 

 ratios found in irradiated flasks by the mean nephelometric ratios 

 found in the dark or check flasks before considering the nephelometric 

 evidence as to algal multiplication under radiation. (See tables 2 

 and 3.) 



