96 Society for Experimental Biology and Medicine. 



lene blue is present. It also applies, perhaps, to solutions of 

 hematoxylin. The staining of the cells in the light as well as in 

 the dark depends also upon the proportions in which both dyes 

 are present in the mixture. 



4. It is possible to distinguish the two factors stated under a 

 and b by killing the cells with heat. The effect of light upon 

 the cells which is caused by its direct action upon the cells, dis- 

 appears if the cells have been previously killed. The changes, on 

 the contrary, which are secondary to the primary changes in the 

 staining solutions are still present. 



5. Means which diminish the oxidative processes in the cells 

 (e. £-., addition of KCN, by which hydrogen is carried through the 

 solution) and saturation of the solution with oxygen, do not modify 

 markedly the differences in the staining of the cells in the light and in 

 the dark. It is, therefore, not probable that the light influences the 

 staining of the cells by causing an increase in the oxidative proc- 

 esses. The addition of alkali to the staining solution is likewise 

 without influence upon the staining of the cells in the dark and in 

 the light. 



6. A series of observations on the behavior of different ova 

 and larvae in the different staining solutions render it probable that 

 the influence of the light depends partly at least upon the injury 

 or death of cells which is caused by light, if the cells are in stain- 

 ing solutions, and that the differences in the action of the stains 

 are therefore secondary. Actively swimming blastulae and gas- 

 trulae stain differently with eosin on the one hand, and with neutral 

 red and methylene blue on the other hand. With the two latter 

 dyes, especially with neutral red, the external layers of healthy 

 cells are stained. With eosin, on the other hand, those cells of 

 blastulae and gastrulae are stained which were cast off either into 

 the inner cavity or to the outside of the organisms. 



