[The hematocrit in the microcirculatory bed of the brain]

Concentration of erythrocytes (hematocrit) was assessed in blood samples taken from small veins of the brain and the hindlimbs of rabbits. Its values were regularly found to be higher by 20% in cerebral vessels than in the hindlimbs. These results corroborate our previous conclusion about preferential distribution of erythrocytes along the arterial ramifications to the brain where the metabolic rate and the blood flow are higher than in other parts of the body. The hematocrit in capillaries of the cerebral cortex was found to be higher than in the veins draining blood from its networks. During ischemia in the cerebral hemispheres the erythrocyte concentration regularly decreased both in the cortex capillaries and in the veins. These changes were independent of the systemic hematocrit, which remained unchanged under these conditions.