1140 BIOLOGICAL EFFECTS OF RADIATION 



13 yeasts. Their conclusion was that differentiation on this basis was 

 impracticable and that nearly all species exhibited fluorescence at 



o 



X3650 A. Giese and Leighton (63) have also studied fluorescence as 

 excited by monochromatic light. It is to be noted that consideration 

 should be given the possibility that fluorescence may be a property of the 

 excretion products of the bacterial cell, therefore, in any examination 

 respecting this property as an intracellular attribute the cells should be 

 washed. On the other hand, fluorescence may be studied in relation to 

 the action of a particular organism on a particular substrate. The 

 fluorescence spectrum of bacteria and fungi under violet and ultra-violet 

 irradiation was studied by Dh^re, Gllicksmann, and Rapetti (31), using 

 both spectroscopic and spectrographic methods. They attribute the 

 fluorescent quality of these organisms to the formation of porphyrins 

 during the course of growth. From Mycobacterium smegmatis, e.g., there 

 was distinguished a strong emission band in the orange, corresponding 

 clovsely with the chief band of copro porphyrin in a neutral medium. 



Photodynamic Effects. — It would appear to be difficult at present to 

 evaluate definitely the influence resulting from the addition to the 

 substrate of substances having fluorescent or "sensitizing" properties 

 upon the physiological effects of visible and ultra-violet radiation. Von 

 Tappeiner and his associates, especially Jodlbauer, (cf. 83, 147) have 

 contributed a series of articles on this subject, and many others (37, 79, 

 98, 141) have extended this field of inquiry. Von Tappeiner and 

 Jodlbauer used a great variety of compounds in such groups as fluores- 

 cenes, anthracenes, quinines, and other dye-furnishing substances 

 primarily absorptive in the visible. They (147) stressed the importance 

 of fluorescing substances and have suggested that some of the earlier 

 studies did not eliminate the possibility of temperature effects. They 

 also present evidence that the photodynamic effect is independent 

 of the production of toxic substances in the substrate, although in general 

 their controls were merely tests in which the fluorescing agents were 

 added to the cultures maintained in the dark. Within the range of 

 visible radiation it was found that the presence of oxygen may be essential ; 

 in the ultra-violet the effect is not dependent upon oxygen (cf. 37). 



According to Dreyer (37), the addition of certain fluorescing sub- 

 stances, notably erythrosin, promotes killing in the yellow and yellow- 

 green, in fact, rendering the bacteria sensitive in this region as well as in 

 the ultra-violet. Erythrosin was considered the best sensitizer with 

 B. prodigiosus. In some of the relatively recent photodynamic work 

 contrary views respecting the significance of such agents have been 

 advanced (141). The relation of dye effects to their absorption spectra 

 has been emphasized (98), and even the bactericidal effect of neon light 

 in the presence of photodynamic agents (Grumback, 67) has been 

 studied. Further systematic, quantitative work is much needed in 



