_Causes and Nature._ The immediate cause and essential lesion of apoplexy has been generally held to be the rupture of an intracranial artery and the formation of a considerable blood clot which presses upon (and abolishes the functions of) the brain. There are cases, however, in which the characteristic symptoms are present, and yet a complete recovery ensues at an early date, too early to allow for the absorption of a considerable clot. Moreover, in fatal cases perhaps no blood clot is to be found, but in place a serous effusion, or an internal congestion which exercised the fatal pressure on the brain. So far, therefore, as clinical phenomena are concerned, we must allow that apoplexy may arise from any sudden pressure on the brain substance. Pagenstecher produced the symptoms of the disease by injecting, at a regulated pressure, melted wax and tallow between the skull and dura mater in the dog. In the moderate cases there were drowsiness, psychic depression and general muscular weakness. In the more severe ones there were added sleep and unilateral paralysis. In the more extreme cases death followed in a few hours after coma set in, though in some of these a partial recovery ensued if the waxy mass was scooped out before the fatal symptoms appeared. Cases ended fatally only when the injection pressure equalled that of the blood, and convulsions occurred only when the pressure was unsteady. The temperature fell as it does in apoplexy in man, at the outset, but it continued falling to the fatal issue contrary to what takes place in man. Duret injected water into the cranium of animals so as to produce great tension of the occipito-atloid membrane causing thereby arrest of the respiration and slowing of the heart’s action. On tearing the membrane so as to allow escape of the water, respiration began anew and consciousness was gradually restored. Edes sustains the view that apoplexy is directly due to anæmia of a lesser or greater portion of the brain substance, and that this need not be in any one particular seat nor of any definite extent. This anæmia is usually induced by pressure and may be caused by effused blood, or serum, or by the extreme congestion due to narcotic poisons, or other cause. Embolism of a cerebral vessel, however, by cutting off the blood from the part of the brain which it supplies may give rise to the apoplectic phenomena.