632 



BIOLOGICAL EFFECTS OF RADIATION 



terize ordinary permeability phenomena (cf. Lucke and McCutcheon, 

 244). 



None of the work considered has taken into account the effects of 

 light of different wave-lengths. The first investigation of this problem 

 is that of M. M. Brooks (45), who worked with the large cells of the alga 

 Valonia macrophysa and determined colorimetrically the penetration 

 of 2-, 6-dibromophenol indophenol into the sap. Her curves show an 

 inverse relation between permeability increase and wave-length (Fig. 1). 

 This permeability increase is independent of the energy transmission of 



the filters used. 



The later results of Lepeschkin (221) agree 

 very well with those of Brooks. He also deter- 

 mined dye penetration, developing a color-com- 

 parison method whereby the intensity of the 

 methylene blue stain in the leaves of Elodea 

 could be translated into percentage concentration 

 per square centimeter of leaf surface per hour. 

 Permeability to the dye was greatly increased 

 by sunlight, but the author found no decrease 

 with protracted illumination. His results with 

 filters harmonize very well with those of Brooks; 

 permeability increase depends more on wave-length 

 than on the amount of radiant energy applied. 

 Fig. 1.— The molecular In studying the penetration of dyes in the light, 



concentration of 2-, 6- ,i p i- ,• j. i j. i ■ j 



dibromophenoi indophenol ^^^ fadmg actiou must be taken mto account, 

 in the sap of Valonia Failure to do this accounts for the contradictory 



(ordinates) when the plants i, r -i-^n m- /c,o\ ^• i x i i • 



had been exposed to screens results of Efimoff (88), accordmg to Lcpcschkm 



(221). _ 



Animal Cells. — The effects of light upon ani- 

 mals are neither so radical nor so obvious as those 

 on plants; the information concerning the effects 

 of light on animal cell permeability is correspondingly less abundant. 

 The most light-sensitive of animal tissues, the retina, was considered by 

 Lange and Simon (210). Frog retina was exposed to a 300-candle 

 Osram lamp at a distance of 80 cm. Following Embden, the authors 

 considered the rate of phosphate production a measure of permeability. 

 This they found to be increased by light, but as a permeability index it is 

 highly indirect, if at all valid. 



Packard (283) used Paramecium in his study of the penetration of 

 NHiOH under illumination. The cells were first stained with neutral 

 red, and the decoloration was taken as a measure of the penetration of 

 the alkali. The injuries due to the alkali are not accounted for but may 

 not be important for relative measurements. Of course, the method 

 assumes constancy of cellular pH during irradiation. Cells irradiated 



transmitting different 

 wave-lengths at intervals 

 up to 10 hr. (abscissas), 

 at 22°C. {After Brooks, 

 44.) 



