LETHAL ACTION OF ULTRA-VIOLET LIGHT ON 

 A UNICELLULAR GREEN ALGA ' 



By FLORENCE E. MEIER 



Division of Radiation and Organisms, Smithsonian Institution 



(With Two Plates) 



INTRODUCTION 



The stimulative and lethal action of ultra-violet irradiation on 

 higher and lower plants and animals has been the subject of interesting 

 research during the past 50 years. Unfortunately, the lack of sufficient 

 physical data makes a correlation of the various results difficult and 

 often inconclusive. 



An accurate determination of the action of ultra-violet light on 

 plants and animals can be obtained only by the use of monochromatic 

 light and by measuring its actual intensity at the surface of the 

 organisms. 



For the work described here a quartz spectrograph was constructed 

 for the purpose of exposing algae under sterile conditions to mono- 

 chromatic light and thereby observing the effectiveness of a wide range 

 of wave lengths in a definite time. This spectrograph was designed by 

 Dr. F. S. Brackett and was constructed in the shop of the Division of 

 Radiation and Organisms of the Smithsonian Institution. A delicate 

 thermocouple ' made possible the unselective determination of the rela- 

 tive energy of the different wave lengths. 



I wish to express my gratitude to Dr. C. G. Abbot, Secretary of the 

 Smithsonian Institution, and to Dr. F. S. Brackett, Chief of the Divi- 

 sion of Radiation and Organisms of the Smithsonian Institution, for 

 their aid and suggestions. The work was done with the cooperation of 

 Dr. E. D. McAlister of the Division of Radiation and Organisms, who 

 carried out the spectroscopic manipulations and physical measure- 



^ This paper reports investigations made under a grant from the National 

 Research Council to the author as National Research Fellow in the Biological 

 Sciences. 



' The thermocouple of special design developed in the Division of Radiation 

 and Organisms, similar to those described in the paper, The automatic record- 

 ing of the infra-red at high resolution, by Brackett and McAlister, Rev. Sci. 

 Instruments, vol. i, pp. 181-193, 1930, was constructed by Dr. E. D. McAlister. 



Smithsonian Miscellaneous Collections, Vol. 87, No. 10 



