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EXPERIMENTAL concussion is a condition well known from the early investigations of Kocher [1901], Duret [1920], Polis [1894] and, more recently, Miller [1927 to be associated with a cessation of respiration and rise of blood pressure, of duration corresponding to the intensity of the blow. Re-investigation of the phenomenon in cats under nembutal anaesthesia confirms its appearance in severe degree, and ability to result in death, without macroscopic lesions of the brain stem. It is further established that the phenomenon can be elicited in the decerebrate animal, and corresponds with a passing depression of all bulbar reflexes (corneal, pinna reflexes, etc.). The respiratory centre is the most sensitive to percussion. Acceleration in movement resulting from the blow is the essential factor in the stimulus, for if the head is prevented from moving when struck the phenomenon fails to occur. Momentary deformity of the skull, and stimulation of superficial structures, therefore appear to play no part. An instant acceleration of the head from zero to 23 feet per second (or reverse deceleration) is the minimal stimulus for the cat. It is slightly higher for the macaque monkey. Labyrinthine stimulation likewise appears to have slight if any part in the phenomenon, for it is obtained after section of both eighth nerves. Rise of intracranial pressure does not accompany the phenomenon, though it is possible under certain circumstances to reproduce a similar effect by a shock-like rise of intracranial pressure alone.The nervous effect of a blow is thus considered to be due to the physical acceleration directly transmitted to each and every centre.

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