Scientific Proceedings. 



95 



ous for cells and for ferments in light than in dark has been previ- 

 ously shown by von Tappeiner, Raab and a number of others. The 

 results of my investigations which were carried out (partly with 

 the cooperation of Mr. L. P. Shippen) in the summers of 1905 and 

 1 906, the last experiment having been done at the end of August, 

 1 906, may be summarized in the following way : 



1. In solutions of dyes (neutral red, eosin, methylene blue, 

 methyl violet and others), cells (eggs of Asterias) are stained differ- 

 ently according to whether the cells and solutions are exposed to 

 the light or kept in the dark. 



2. Combination of an acid and a basic dye (eosin and methy- 

 lene blue) increased markedly the differences in the staining of the 

 cells in the light and in the dark, in so far, as a small addition of 

 methylene blue to eosin suffices to increase very much the staining 

 reaction which is characteristic for light. The same holds good, 

 probably, for other combinations, as neutral red and eosin. A 

 mutually neutralizing or antitoxic effect of basic and acid dyes 

 does, therefore, not exist. This increase in the effect of a combina- 

 tion of methylene blue and eosin is not caused by a primary change 

 which the light produces in the solutions. Solutions of dyes 

 which have been previously exposed to light do not stain the cells 

 in the dark differently from solutions which had not been exposed 

 to the light. In a combination of two basic dyes (methylene blue 

 and neutral red) methylene blue and neutral red substitute each 

 other in the dark according to the proportions in which they are 

 mixed. In the light the cells assume a tone intermediate between 

 neutral red and methylene blue. 



3. The difference in the staining of cells in the light and dark 

 is caused by at least two different effects of the light, (a) The 

 light causes primary changes in the cells, and the difference in the 

 staining of cells in the light and in the dark is caused by those 

 primary changes which the light produces in the cells. This 

 applies to staining with eosin, neutral red and with certain mixtures 

 of eosin and methylene blue and eosin and neutral red. (b) The 

 light changes primarily the staining solutions and the staining of 

 the cells corresponds to the primary changes in the staining solu- 

 tions. This applies to staining with pure methylene blue and to 

 such mixtures of methylene blue and eosin in which much methy- 



