ABSORPTION FROM THE VENTRICLES 317 



the central canal. The inner portion of the zone of staining 

 adjacent to the ventricles was most deeply colored, while towards 

 the surface of the brain the stain became gradually paler. It is 

 noteworthy that the stains had penetrated even into the most 

 caudal recess of the central canal of the cord (fig. 2). 



Microscopically, the dyes were readily visible in the tissues of 

 the brain. Precipitated Prussian-blue granules were found in 

 the tissues surrounding the ventricles. The precipitate occurred 

 in the intercellular spaces, in the perineuronal spaces and 

 to a large extent in the perivascular sheaths. Prussian blue 

 was precipitated in minute granules in the cytoplasm of the epen- 

 dymal cells. None of the precipitate was found to be intracellu- 

 lar, either in glial or nerve cells. The choroid plexuses did not 

 appear to have been penetrated by the coloring matter. 



The distribution of trypan blue differed microscopically some- 

 what from that of the Prussian blue. The choroid plexuses 

 appeared entirely unstained. Precipitated trypan blue was 

 visible on the surface of the ependymal cells in some areas, 

 but none was discernible in the cytoplasm of the cells. Trypan 

 blue could not be seen in the intercellular spaces or in the perineu- 

 ronal spaces. Many of the glial cells contained dust-like parti- 

 cles of dye within their cytoplasm. Trypan blue was not visible 

 in the cytoplasm of any of the nerve cells. The small vessels 

 and capillaries in the zone of staining were noteworthy in the 

 trypan-blue animals. Brilliantly stained cells containing nu- 

 merous granules of the dye in their cytoplasm everywhere sur- 

 rounded the blood-vessels (fig. 4). These cells which closely 

 invest the blood-vessels belong to the category of adventitial 

 cells or macrophages. They are extremely phagocytic and are 

 the scavenger cells of the brain tissue, which have been repeatedly 

 shown to play a prominent role in brain injury and repair. 



The microscopic distribution of these substances indicates that 

 they have followed definite pathways in their escape from the 

 dilated ventricles. The solutions are observed in their escape 

 through the ependyma into the intercellular spaces and thence 

 into the perivascular sheaths. These observations lead to the 

 conclusion that fluid currents exist between the dilated ventricles 



