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LETHAL RESPONSE OF THE ALGA CHLORELLA 

 VULGARIS TO ULTRAVIOLET RAYS ' 



By FLORENCE E. MEIER 

 Division of Radiation and Onjanisms. Smithsonian Institution 



(With Three Plates) 



INTRODUCTION 



In a previous paper Meier (1932) reported a quantitative study 

 of the lethal effect of the wave lengths 3022, 2967, 2894, 2804, 

 2753, 2699, 2652, and 2536 A on the unicellular green alga Chlordla 

 vulgaris. Wave lengths longer than 3022 A, which is the approximate 

 short-wave limit of ultraviolet irradiation in nature — that is, the wave 

 lengths 3130, 3341, and 3650 A— had no lethal effect on the green 

 cells, although two of them, 3130 and 3650 A, were of greater in- 

 tensity than the shorter lethal ones. 



The present paper gives the results of further study on the lethal 

 response of the alga Chlordla vulgaris to the same ultraviolet wave 

 lengths with special reference to the radiotoxic spectral sensitivity 

 and the radiotoxic virulence. 



This work was done with the cooperation of Dr. E. D. McAlister, 

 of the Division of Radiation and Organisms, w'ho carried out the 

 spectroscopic manipulations and physical measurements. 



I wish to express my appreciation to Dr. C. G. Abbot, Secretary 

 of the Smithsonian Institution, for his assistance in the interpretation 

 of the results of these experiments and for suggesting the new terms 

 here used. I am also grateful to Dr. E. S. Johnston, Assistant Director 

 of the Division of Radiation and Organisms, for his help in the ac- 

 complishment of this piece of research. 



RECENT INVESTIGATIONS 



Striking work requiring nice technique on the lethal action of ultra- 

 violet irradiation on certain living Protozoa has been done recently 

 by the Cancer Research Laboratory at the L^niversity of Pennsylvania. 



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

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

 Sciences. 



Smithsonian Miscellaneous Collections, Vol. 92, No. 3 



