The circulation may be merely disturbed, or laceration of the brain may occur with extravasation of blood into its substance. It may present the appearance of having been bruised, or the tear of its substance may be extensive. A multitude of minute vessels may be torn without the substance of the brain being much broken, in which case bloody specks will be observed over a large surface of the interior of the organ. In many fatal cases no change in the state, either of the vessels or of the cerebral substance, is perceptible on minute examinations. The organ in these cases has been merely disturbed and shaken, without visible rupture or hurt having occurred. Again, many patients are supposed to labour under concussion only, in whom fracture of the base of the cranium, or extravasation of blood on the surface, or into the substance of the brain, are discovered after death. It is always difficult to distinguish between the effects of mere concussion and those of compression of the brain by extravasated fluid; for, in the greater number of cases, the symptoms of both affections are blended together. In both there is insensibility from the first; but if an interval of sensibility occur, diagnosis is rendered more easy and certain, it being a fact well verified by experience, that the state of stupor which precedes the return of correct intellectual function is the effect of concussion, and that there is every reason to believe that the insensibility into which the patient subsequently sinks, is caused by compression of the brain; if compression existed from the first, the stupor might not be of longer duration than if it were the effect of concussion, but its stillness would not be interrupted by any restoration of mental exercise, however short. Remarkable effects sometimes result from commotion of the brain; the patient may suffer loss of vision or of hearing, either partial or complete; or partial paralysis may occur; of the muscles, for instance, supplied by the portio dura. In many cases such affections may be supposed to arise from compression of nerves, or other læsion subsequent to and caused by the effects of concussion, and probably connected with fracture of the base of the cranium. Again, it occasionally happens that the senses are rendered more acute than previously, and of this I shall mention an example which came under my own observation. An old nurse sustained fracture of the vertex, with slight depression of the broken part, in consequence of some rubbish having fallen on her from a considerable height. Stupor, along with the other symptoms of concussion, was the immediate effect of the injury, but disappeared in two or three days. Her hearing, which previously to the accident had been long so obtuse as to render it necessary for her to discontinue her employment, became so intensely acute, that the most trifling noise became a source of pain. She gave immediate orders for the clock