890 BIOLOGICAL EFFECTS OF RADIATION 



has been little study of the effects of different light intensities on pig- 

 mentation. Smith and Swingle (170) reported that within the limits used 

 in their experiments color appears sooner in the mycelium of Fusarium 

 oxysporum with the highest light intensities. They also found that 

 after the light-color response any new growth of the mycelium in dark- 

 ness is white, indicating that the effects produced by light cease almost 

 as soon as the light is removed. Experiments made by Smith and 

 Swingle (170), Bessey (6), Robinson (159), and McCrea (119) all show 

 that pigment production is induced by the blue end of the spectrum, 

 and McCrea's results show in addition that red rays exert no inhibiting 

 effect. In all these experiments liquid light filters were used. The 

 culture medium may also influence the degree of pigment production 

 or may even determine whether pigment is formed. Such results 

 have been reported by Smith and Swingle (170) and by Morris and 

 Nutting (127). 



Growth Rate. — Sunlight has long been known to exert an inhibitive 

 effect on the growth rates of fungi. Qualitative studies have been made 

 by Fries (52), Carnoy (20), Brefeld (15, 16), Downes and Blunt (35), 

 Pfeffer (145), Stameroff (172), Zopf (cf. Elfving, 39), Kegel (155), Vines 

 (189), Ternetz (187), Schulze (167), Lieske (105), and Potts (148). 

 Small amounts of sunlight retard whereas large amounts kill fungi. 

 Qualitative studies have also been made of the retarding effects of ultra- 

 violet radiation. Among these might be mentioned those of Lieske (105), 

 Porter and Bockstahler (147), Dillon- Weston and Hainan (34), Welch 

 (192), and Feuer and Tanner (51). 



Attempts were next made to show which regions of the spectrum 

 exert harmful action. Kegel (155), Vines (189), and later Buchta (18), 

 all using liquid filters, found that it is the blue end of the visible spectrum 

 that retards growth. It was also found by Lieske (105), Buchta (18), 

 and others that the ultra-violet is more harmful than the blue. In 

 studying different regions of the ultra-violet Johnson (83), Hutchinson 

 and Newton (80), and Hutchinson and Ashton (79) reported that the 

 shortest wave-lengths appear to be the most harmful. Johnson used 

 glass filters, and Hutchinson and Newton, and Hutchinson and Ashton 

 used a monochromator, but the intensities were not measured for the 

 different wave-lengths studied so that a final evaluation of the results 

 is provisional. More recently, however, two papers have appeared, 

 one by Ehrismann and Noethling (37) and the other by Oster (141), 

 in which careful studies have been made of the effects of equal intensi- 

 ties of different wave-lengths in the ultra-violet on the growth of yeast 

 cells. In both studies monochromatic light was used and the intensities 

 were measured with a photoelectric cell or thermopile. Ehrismann and 

 Noethling considered the energies necessary to produce 1 to 10 per cent 

 killing, whereas Oster considered 50 per cent killing. However, when 



