The work of Cushing1 on intracranial pressure, published in 1902, brought out an important mechanism of adjustment in the body. He found experimentally that as intracranial pressure was gradually raised toward the level of the blood pressure, the blood pressure rose enough to keep ahead of it and to keep the brain sufficiently supplied with blood so that respiration continued. On the other hand, when intracranial pressure was raised suddenly, respiration would cease temporarily, following which the blood pressure would quite rapidly climb above the pressure of the cerebrospinal fluid, and respiration would begin again. Vagus effects, shown by slowing or stopping of the heart, were observed unless the intracranial pressure was increased very gradually and slowly. Meanwhile, by means of a window in the cranium of the dog, the pialvessels and the superior longitudinal sinus were observed. As the intracranial pressure was raised, increasing evidence of stasis and