VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 567 



in cells exposed to monochromatic red light. It became greater as the 

 wave lengths shortened and was greatest in the near-ultraviolet range. 

 The duration of light was also an important factor. When paramecia 

 were kept in darkness for 2 hr or more and then exposed to light for 

 periods ranging from 1 to 5 hr, it Avas found that the velocity of color 

 change increased rapidly after a 1-hr exposure and then more slowly, 

 until after 5 hr there was practically no further increase. 



Brooks (1927) studied the absorption of 2,4-dibromophenolindophenol 

 in light of different wave lengths (300-700 van). Valonia macrophysa 

 was used as the test object and placed in glass dishes containing a 

 0.00035 M solution of the dye dissolved in sea water. The dishes were 

 then placed in larger pans, whose tops were screened with glass screens of 

 different colors (red, green, or blue) or i^ncolored, and the pans placed in 

 diffuse daylight. After the end of 1, 3, 5, and 10 hr, a number of plants 

 were removed and tested by analyzing the cell sap. It was assumed that 

 equilibrium conditions were set up between the external solution, the 

 protoplasm, and the sap at the end of the experiment. The results 

 showed that the amount of dye in the sap increased as the wave length 

 of the incident light decreased toward the ultraviolet end of the spectrum. 

 Thus, the results obtained by Brooks (1927), Packard (1925), Lepeschkin 

 (1930, 1932a, b,c), and Jarvenkyla (1937) are in agreement with regard 

 to the association between the influence of light and the wave length. 



Experiments with Absorptio7i of Poisonous Substances. Kahho (1921) 

 treated sections of red cabbage with solutions of salts with a slightly 

 poisonous effect (sodium iodide, sodium bromide, and sodium thiocya- 

 nate) and determined the number of damaged or dead cells with the 

 plasmolytic method. In a comparison between sections treated in the 

 light and those which had remained in the dark, it was found that damage 

 to the cells was more extensive in the former case. This was interpreted 

 by Kahho as an indication that Hght increased the permeabihty of the 

 cells to the salts in question. 



It is not only the permeability of the protoplasm of plants and lower 

 animals which is influenced by light. Lepeschkin (1932c, 1933) found 

 similar reactions in the erythrocytes of animals and man. Light pro- 

 duced a greater intake of glycerol into the erythrocytes, resulting in a 

 more rapid swelling and hemolysis of the cells than when the erythrocytes 

 were kept in the dark. When exposed to light, human erythrocytes 

 absorbed more glucose and increased more in volume than in the dark. 

 The permeability to sodium chloride was also found to be weaker in the 

 dark. 



Experiments with the Method of Electrical Resistance. Rapid methods 

 are of great importance for a study of the relation between light and 

 permeabihty. If, for example, the permeability is affected by the changes 

 in viscosity induced by light or by other processes associated with them, 



