566 RADIATION BIOLOGY 



and that of the viscosity on light is evident. Also, for the influence of 

 light on the viscosity, the pretreatment of the ol)ject is of decisive 

 importance. 



Expemnenis with Absorption of Dyes. Measurements or estimations 

 of the ability of the cell to absorb dyes have been used in studies of the 

 association between permeabihty and the influence of light. The method 

 is simple and convenient but unfortunately involves the risk of confusing 

 the effects of permeabihty and the ability of the cell to store the dye. 

 The cell contents may show strong stainability on the grounds not only 

 of good permeability but also of the great ability of the cell to bind or 

 precipitate the dye. 



Segel (1915) used this method to study the permeability of Elodea 

 densa in light and in darkness. He found that light promoted the intake 

 of methylene blue and of neutral red. The experiments covered a period 

 of 3-8 hr. Efimoff and Efimoff (1925), who made similar experiments 

 with a number of dyes, found that only methylene blue was absorbed in 

 light more markedly than in dark. But according to Lepeschkin (1930), 

 he did not consider the chemical changes in anihne dyes to be produced 

 by light. All those dyes in the Efimoffs' experiments which failed to 

 show any effects of light are particularly sensitive to it. 



Lepeschkin (1930, 1932a, b), who used the same method, covered part 

 of the leaves of Elodea with tin foil so that the same leaf could be exposed 

 simultaneously to light and darkness. In this case as well, the intake of 

 dyes was enhanced by light. Staining after a longer period (100 min) 

 gave the same results in both types of plants, whereas initially stain- 

 ability was greatest in the plant exposed to light. Lepeschkin therefore 

 considered this as proof that the stronger stainability of the object or 

 part of the object exposed to light was actually due to an increase in 

 the permeability and not to an increase in the storing ability of the cell. 



The rays most active in producing the increase in permeability were 

 those with a wave length of 320 420 m^; violet rays were less active, 

 blue and green still less active, and red rays the least active. 



Packard (1925) stained paramecia with neutral red and then trans- 

 ferred them to a weak solution of ammonium hydroxide. As the ammo- 

 nia entered, it changed the red granules to yellow at a rate that was 

 constant under definite conditions. In the ammonia all the cells did not 

 lose their red color simultaneously. If the process was watched under a 

 binocular microscope, each cell could be pipetted off as soon as it was 

 decolorized and the time noted which had elapsed after it had been put 

 into the ammonia. When all the cells had been withdrawn, the average 

 time for decolorizing the total number was calculated. The experiments 

 showed that light was an important factor in producing changes in the 

 permeability of Paramecium to ammonium hydroxide. In light the 

 permeability was greater than in darkness, the change also being found 



