EFFECTS OF RADIATION ON FUNGI 891 



wave-lengths are plotted against the energies neressary to kill, the 

 curves are essentially similar with minima at about 2650 A. Ehrismann 

 and Noethling worked only with wave-lengths above 2400 A. Oster 

 worked with wave-lengths as low as 2200 A, and his curves indicate 



o 



another minimum below 2300 A. It is interesting to note that these 

 curves are comparable in shape with curves which have been obtained 

 for bacterial cells. A comparison made by Oster of the energies neces- 

 sary to kill 50 per cent of the cells irradiated shows, however, that 



o 



457 erg mm.^ are necessary at 2652 A compared with 23,500 ergs mm.^ 

 at 3022 A, or roughly five times the energy range which has been obtained 

 for Staphylococcus aureus. The curves are also similar to those of certain 

 nucleoprotein derivatives known to occur in yeast cells. Oster pointed 

 out that this suggests that possibly the effects of ultra-violet radiation 

 may result from the absorption of energy by these nucleoproteins. 



A number of recent papers have laid much emphasis on the differ- 

 ent degrees of injury which may be produced by ultra-violet radia- 

 tion. This is not a new idea. Schulze (167) as early as 1909 reported 

 that when Mucor stolonifer is irradiated with diffuse light of 2900 A, 

 there is — except with strong intensities — an interval or latent period 

 before growth is hindered. If the hyphae are irradiated until growth 

 stops, there is no further growth, but if the irradiation is not continued 

 so long, growth often stops sometime after irradiation but is resumed 

 again after a period of no growth. Lacassagne (96) divided yeast cells 

 which had been exposed to ultra-violet radiation into three classes; 

 (a) cells which after a retardation in cell division ultimately recover 

 their reproductive powers; (6) cells which divide only once and then die; 

 (c) cells which die without dividing. Wyckoff and Luyet (196) and 

 Oster (139) have also placed yeast cells in these different categories, 

 but Oster considers an additional class which falls between (a) and (6) 

 in which the metabolic functions of the cell are retarded as shown by a 

 lowered rate of oxygen consumption. 



In the early studies of the retarding effects of radiation on growth 

 rates no absolute measurements were made of the intensities of light 

 used. However, comparisons were made of the different exposures 

 to the same intensities necessary to produce the same effect in differ- 

 ent fungi and to produce different effects in the same fungus. Von 

 Recklinghausen (190) found that it took more than six times as long 

 to kill yeasts as to kill bacteria in water, and Houghton and Davis (78) 

 made observations on the marked resistance to ultra-violet of molds 

 as compared with bacteria. Dillon-Weston and Hainan (34) showed 

 that increasing the intensity increases inhibitive and lethal effects. 

 More recently absolute measurements of intensity with a thermopile 

 or photoelectric cell have been made by Wyckoff and Luyet (196), 

 Ehrismann and Noethling (37), Schreiber (166), and Oster (139). The 



