Our previous studies have shown that when one area of the hemisphere of the cat brain has been exposed to the air for a few hours after the dura has been opened, an acute reaction takes place. It was found that although this reaction is more pronounced in the exposed area, more remote regions in both hemispheres, as well as the subcortical structures, are also affected.
The pathologic changes in the reaction of the brain tissue have been described.1 In its earliest phases a vasodilatation takes place, which reaches its maximum about two hours after the beginning of the exposure; by that time the pulsations of the brain disappear, and a certain degree of cerebral swelling may be noticeable. Intravenous injection of trypan dyes given immediately after the exposure reveals an increase in the permeability of the blood-brain barrier, as shown by the diffuse staining of the brain with