EFFECTS OF RADIATION ON BACTERIA 1141 



tliis fiold, but it .should he recognized at the outset tluit the photochemical 

 reactions may be compUcated, and accurate interpretation correspond- 

 ingly difficult. 



Remarks. — In so brief a review of the effects of radiation on bacteria 

 many relevant topics are necessarily left out of consideration. Observa- 

 tions on the effects of radium are sufficiently extensive to justify inclusion, 

 although largely qualitative. Moreover, a special paper of this work 

 (Gager, Paper XXX) is devoted to the general effects of radium on 

 plants. Wyckoff and Rivers (167) have studied the influence of cathode 

 rays, and the action of polarized light (15, 59) has not been neglected. 

 Bacterial luminescence is a large problem and phototaxy an interesting 

 one, but both have been looked upon as outside the province of this 

 article. Many investigators have given some attention to the con- 

 sequences of sublethal irradiation of pathogenic bacteria, and it is well 

 known that modifications of pathogenicity may occur, but until quantita- 

 tive work has been done in this direction the picture is scarcely more 

 than outlined. To the reviewer it appears also that the most attractive 

 lines of work await the investigator — in general, the modification of rate 

 or quality of such physiological relations as fermentation and metabolic 

 products, respiration, pigment development, and growth behavior, as 

 well as modification of cell or colony form and the influence on spore 

 formation and on genetic expression. Finally, it would be instructive 

 to- attempt to give a comparative review, at least in relation to proteins, 

 enzymes, viruses, protoplasm, bacteria, and other unicellular organisms. 



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