Diffusion and Absorption Within the Brain

Abstract

10 rabbits and 9 cats were anesthetized and injected in various parts of the brain with an apparatus built and descr. by the author. A 10% soln. of equal parts of Fe, NH4CI, and K3Fe(CN)6 was used for 8 bilateral injns. in rabbits and for all injns. in cats. A soln. of equal parts of Fe, NH4CI, and K3Fe(CN)6 was mixed with the same quantity of India ink for all other expts. except for 1 rabbit in which India ink alone was used bilaterally. In order to prevent leakage of the injected material to the surface of the brain, the tract and cavity were sealed using a coagulating current as the needle was withdrawn to the surface. This technic was used for 3 of the rabbits and for all of the cat expts. Rabbits were sacrificed from 0.5-3.5 hrs. and cats from 1-9 hrs. following injn. The most satisfactory technic for sacrifice was guillotining which prevented terminal edema. Sections 8u in thickness examined under oil immersion with a strong light were the best prepns. for distinguishing the distr. of injn. material. Thus infiltration from the subarachnoid spaces into the cortex is seen only in extreme conditions of stagnation and massive invasion. There was little diffusion in the cortex with its numerous absorbing vessels. In the basal areas of the cortex these actively absorbing vessels prevent the penetration of substances from the white matter. In the white matter diffusion is widespread along the course of the glial fibers. There is absorption all over the area extending to the center of the hemisphere and especially by the internal cerebral vein. From the ventricular system absorption appears to take place through the ependyma and sub-ependymal tissue but not through the choroid plexus. Passage of material along the perivascular spaces appear to be minor.