IRRADIATION OF LIVIXG PROTOPLASM 633 



with sunlight through glass were more permeable than those kept in the 

 darkness. By the use of filters, Packard also obtained results agreeing 

 with those of Brooks and Lepeschkin; the shorter wave-lengths had 

 relatively more effect upon the permeability. 



Increased intensity of stain in both nucleus and cytoplasm of frog 

 leucocytes in Nile blue sulfate when irradiated with a 32-candle Osram 

 lamp was found by Haberlandt (126). Disappearance of the color with 

 protracted illumination, however, renders difficult any reading of a 

 permeability factor into these results. 



Recently Lepeschkin (224) has presented data showing an increase 

 of the permeability of human and cow erythrocytes to electrolytes and 

 nonelectrolytes under the influence of sunlight. He used three methods: 

 (a) hematocrit, (6) osmotic hemolysis, and (c) isotonic coefficients based 

 on the use of a penetrating and a nonpenetrating hypotonic solution to 

 cause hemolysis. By the first method he determined the relative perme- 

 ability of the blood corpuscles to glucose; by the second, permeability 

 to glycerin; and by the third, the permeability of cow erythrocytes to 

 NaCl and the permeability of human erythrocytes to glucose. In all 

 cases light caused an increase in the rate of penetration, whether of dis- 

 solved substance or water, although the results are not translated into 

 absolute terms. 



In all, then, the evidence favors the view that visible light increases 

 the permeability of plant and animal cells. The chief objections arise 

 from the experiments of Kisselew and of Zycha. The former used only 

 the very specialized guard cells; the latter's results are open to the criti- 

 cism of Lepeschkin, already mentioned. The newer and semiquantita- 

 tive data render a conclusion fairly safe, though the methods of control 

 of radiation quality and intensity allow no quantitative comparisons. 

 Even for plant cells there is yet no single set of experiments that com- 

 bines a reliable permeability method with accurate determination of 

 the illumination. 



ULTRA-VIOLET RAYS 



The literature on changes in permeability produced by ultra-violet 

 rays is much smaller than that on the visible spectrum. The work is 

 largely on animal cells, for which, unfortunately, the methods of exact 

 permeability measurement are limited to a few types of material. 



The work of Brooks and of Lepeschkin, which contained evidence for 

 a permeability increase in plant cells by the ultra-violet portion of ordi- 

 nary sunlight has already been cited. These authors made no experi- 

 ments using artificial sources. 



The " radiopuncture " method of Tschachotin (364 for method proper; 

 357), by which a beam of ultra-violet rays is focused on a single cell or 

 part of a cell, has given this author results interpreted as evidencing a 



