UNIVERSITY OF CALIFORNIA PUBLICATIONS 
IN 
PATHOLOGY 
Vol. 2, No. 21, pp. 245-250 March 25, I9I9 
THE ACTION OF ULTRAVIOLET LIGHT ON 
CERTAIN BACTERIA IN RELATION 
TO SPECIFIC ABSORPTION 
BY AMINO ACIDS 
BY 
FRANKLIN I. HAERIS and HUBBARD S. HOYT 
(From the Department of Pathology and Bacteriology, University of Caiifornia) 
Within recent years considerable interest has been shown in 
the study of the ultraviolet radiations in relation to their toxicity 
for living protoplasm. It was early found that these radiations 
exert a highly toxic influence on protoplasm exposed to them. 
Henri,'' - in conjunction with various co-workers, has done 
pioneer work in this field, and was the first worker to point out 
the possibility of a practical application of this subject, namely, 
in the sterilization of various substances and solutions. Further 
work on the germicidal effect of ultraviolet light has been done 
by Houghton and Davis,^ who found that the rays produced by 
the Cooper-Hewitt mercury arc exert a strong bacterial action 
on various species of bacteria, including spore forming organisms. 
The action of these radiations was recognized as a photo- 
chemical process, and was supposed to be due to the absorption of 
the rays by the bacterial protoplasm. In a previous report^- ^ 
we studied this phase of the problem and proceeded on the basis 
of the first law of photochemical action, that in a photochemical 
system, to be effective, the rays must be absorbed, usually by 
specific constituents. We h.nve further shown that the toxic 
