CELL DIVISION, MORPHOLOGY, VIABILITY 811 



and in which, therefore, penetration of the radiation is not a serious 

 problem. 



MITOTIC EFFECTS 



Nature of Effect. Reduction of mitotic activity immediately following 

 treatment with mixed wave lengths of ultraviolet radiation has been 

 described for chick fibroblasts in vitro (Kemp and Juul, 1932; Juul and 

 Kemp, 1933; Mollendorff and Laqueur, 1938), marine invertebrate eggs 

 (Nebel, Harvey, and Hollaender, 1937; Chase, 1938; Blum et al., 1949; 

 Blum et al., 1950; Blum and Price, 1950), salamander corneal eipthelium 

 (Politzer and Alberti, 1924) and rat corneal epithelium (Buschke, 

 Friedenwald, and Moses, 1945). After monochromatic radiation, divi- 

 sion of the marine invertebrate egg is retarded by various wave lengths of 

 2260-3130 A inclusive (Hertel, 1905; Nebel et al., 1937; Giese, 1938a, b, 

 1939a, b, c, 1946; Marshak, 1949; Wells and Giese, 1950). Mitotic 

 activity is reduced in the rat corneal epithelium by wave lengths 2480 

 through 3160 A (Friedenwald et al., 1948). In the grasshopper neuro- 

 blasts, only 2250 and 2537 A have been studied in detail and found to 

 retard division (Carlson and Hollaender, 1944, 1945, 1948) but pre- 

 liminary experiments indicate that longer wave lengths, up to and 

 including 3130 A, are probably also effective. 



Comparative studies of the effectiveness of different wave lengths 

 point to the 2480-2804 A region inclusive as producing the greatest 

 retardation of mitosis (Mayer and Schreiber, 1934; Giese, 1938b, 1939a, 

 b; Friedenwald et al., 1948). Giese (1946) found that treatment of cer- 

 tain echinoderm sperm gave an action spectrum for delay through the 

 third cleavage that resembles the absorption spectrum of nucleoprotein 

 (high at 2600 A), while treatment of the unfertilized egg gave an action 

 spectrum resembling protein (high at 2800 A) . He suggested that cleav- 

 age may be slowed by different types of induced changes in the sperm and 

 egg. Friedenwald et al. (1948), however, found that the action spectrum 

 for mitotic activity in the rat corneal epithelium was high at 2480 and 

 2804 and lower at 2650 A. 



Of the tissues so far examined only periblem cells of the root tip of 

 Vicia have given evidence of an increase in the percentage of cells in 

 mitosis immediately after treatment with ultraviolet radiation. Taka- 

 mine (1935) found that after exposure of one side of root tips to the radia- 

 tions from a quartz mercury vapor lamp, 2-3 hours after an exposure of 

 3^-3 hours, the percentage of cells in mitosis (prophase, metaphase, 

 anaphase, and telophase) on the exposed side of the root tip was about 

 1 per cent higher than on the opposite side. Subsequently, the percent- 

 age on the treated side fell until at 15 hours it was about 1 per cent less 

 than the control side; and the percentage was still below normal at 48 

 hours. The effects of monochromatic radiation of 2537 and 3650 A were 



