318 G. B. WISLOCKI AND T. J. PUTNAM 



and the neighboring vessels, under the abnormal conditions of 

 a heightened intraventricular pressure. 



It remains to be pointed out that there is no evidence micro- 

 scopically that the substances behave as a fixative would if 

 similarly injected. Neither of the reagents employed in these 

 experiments appears to exert any deleterious influence on the 

 cells which it encounters during its passage into the brain tissues. 

 Nuclear staining or diffuse discoloration of the brain tissue, 

 which would be indicative of cell injury and death, are not 



Fig. 4 Microscopic section of the cortex of the left hemisphere of a rabbit in 

 which trypan bhie had been injected into the dilated ventricles. A portion of a 

 small cerebral vessel is shown, surrounding which are several phagocytic cells 

 containing granules of trypan blue. 



observed. The phenomena of distribution of the dye granules 

 must be looked upon not as the result of diffusion of a foreign 

 chemical through dead tissue; but as a true passage of the dyes 

 through the brain tissue during life. The explanation for the 

 different findings with the ferrocyanide-citrate solution and with 

 the trypan blue lies in the fact that microscopic identification 

 of the former requires only the action of the mineral acid, w^hile 

 vital activity on the part of a certain class of phagocytic cells 

 is necessary for the intracellular aggregation of the vital-dye 

 particles before microscopic identification is possible. As 

 illustrating microscopically the pathway of absorption, the 



