The brain serves as a centre for voluntary motion and for the perception of sensory im pulses. It follows that injury to or disease of the brain is frequently followed by paralysis of greater or less extent. Thus concussion of the brain: fracture of the skull with resulting com pression due to displaced bone or to hemorrhage in the cranium; hemorrhage into the substance of the brain or into its membranes independent of external injury; compression of the brain from tumors benign or malignant. from syphilitic gummata, etc.; destruction of brain tissue by extension of disease from surrounding parts. as from hone necrosis, middle ear disease. abscesses, etc.; hrain-softenin7 from cutting off blood sup . • • -is in thrombosis or cmholism—all these and other widely different le-ions cause paralysis as a symptom by interfering with the proper work imr of the nervous mechanism.
There remain to be described somewhat more in detail certain conditions to which the term paralysis is popularly applied.
IlLAIIPLEGIA is that form of paralysis popu larly known as a 'paralytic stroke' or 'stroke of apoplexy.' The paralysis affects only one lateral half of the body. The parts generally affected are the upper and lower extremities, the muscles of mastication, and the muscles of the tongue on one side. In a well-marked case the patient when seized falls to the ground, all power of motion in the affected arm and leg being lost. The paralysis of the face which accompanies hemiplegia is usually quite distinct from the affection known as facial paralysis, which is au affeetion of the facial nerve or portio dura. (See
NERVOCS SYSTEM AND BRAIN.) The motor branches of the fifth or trifacial nerve going to the muscles of mastication are generally involved in hemiplegia, and consequently the cheek is flaccid and hangs clown, and the angle of the mouth is depressed on the affected side. The tongue when protruded points toward the par alyzed side, and there is often imperfect articula tion, in consequence of the lesion commonly affecting the hypoglossal nerve. While paralysis of one side of the body or hemiplegia may be due to a large number of different conditions in the brain or cord, some of which have been already mentioned, it is most commonly due to one of three cerebral accidents. These, mentioned in the order of frequency of their occurrence, are (I) cerebral hemorrhage, (2) cerebral embolism (q.v.), (3) cerebral thrombosis (q.v.). Hemor rhage may occur into any portion of the brain tissue proper or between the skull and brain. i.e. into the meninges. These hemorrhages may be clue to injury to the vessels or to disease of the ves sel walls such as athcroma or aneurism. The most common seat of hemorrhage is in the optic thalamus and corpus striatum, from the branches of the middle cerebral artery. With the escape of blood there is usually more or less tearing and destruction of brain tissue. and this broken down brain tissue mixed with the extravasated blood constitutes what is known as the apoplectic clot.