The progressive changes of the brain tissue around the experimental intracerebral hematoma which was made stereotaxically at the lateral portion of the internal capsule of the dog, were observed histologically. Half hour after making the hematoma, sponge-like change of the brain tissue was found around the hematoma. Six hours after, three layers of the changes were observed. The inner was the necrotic layer in which red blood cells infiltrated, the middle was the layer with perivascular

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... s and the outer was the layer with sponge-like change. Each change was increased progressively. These histological changes of the brain tissue around the hematoma were stronger at the middle-upper side of the hematoma where the internal capsule was situated. Then it is concluded that the hypertensive intracerebral hematoma (lateral type) should be evacuated within 6 hours after the onset for its good prognosis.