This ‘latent’ period lasts for a variable period of time--seldom less than a week or more than three months. At the end of that time the picture changes, and the patient evidences symptoms obviously referable to local brain compression. From a clinical point of view it is fortunate that subdural hæmatoceles tend to involve the fronto-parietal region with the consequent development of motor symptoms, especially paresis or paralysis of the contra-lateral side. Hence the name sometimes applied to the condition--traumatic late apoplexy. The speech areas are implicated if the injury be situated on the left side. Paralysis limited to the lower extremity is exceedingly suggestive, such a palsy occurring only with the greatest rarity in extra-dural hæmorrhages (from the middle meningeal artery). If the pressure be unrelieved by operation the patient passes from the excitatory to the paralytic stage of brain compression, gradually falling into a condition of coma, the pulse increasing in frequency and the respiration becoming more and more embarrassed. In the study of this condition, the following are the points to which special attention should be paid:-- 1. The comparative want of severity with respect to the injury received. 2. The absence of any ‘lucid’ interval, such as is present, for example, in middle meningeal hæmorrhage. 3. The presence of a definite ‘latent’ period. 4. The late development of symptoms pointing to general and local brain compression. Finally, it may be stated in general that the more indefinite and the more deferred the pressure symptoms, the greater the probability that we have to deal with a localized subdural hæmorrhage. Lumbar puncture may materially aid in the differential diagnosis between extra-dural and subdural hæmorrhages. The following case affords a typical example of subdural hæmatocele:-- An elderly man fell down, striking the right side of the head against the pavement. He lost his senses for a few minutes and was then brought to the hospital, dazed and complaining of headache (note the absence of any _lucid_ interval). He was sent home in a cab and was assisted to bed by his wife. He kept to his bed during the next week, complaining of constant headache, and was exceedingly irritable (this is the ‘latent’ period). Towards the end of the third week his wife noticed that he seldom used the left upper and lower extremities. This paresis increased steadily, the face was drawn to the right side, and his condition became so serious that the wife brought him again to the hospital (this is the ‘manifest’ period).