Page:The American Cyclopædia (1879) Volume III.djvu/204

 198 BRAIN (DISEASES) but a slight remove from death. Prolonged syncope may occasion sudden death ; but in general, after a brief period, the circulation within the skull is restored, and consciousness returns. The cerebral anaemia in attacks of syncope is usually caused by a suddenly in- duced weakness of the heart's action, and this may be occasioned by various causes. A pow- erful mental emotion may so affect the action of the heart as to cause an attack of syncope. The rapid loss of blood is a cause. Assuming an erect posture after recumbency from disease is another cause. Impoverishment of the blood, or the morbid condition of this fluid known as ancemia, favors the operation of the different causes which, by enfeebling the action of the heart, gives rise to syncope. The measures to be employed in syncope are those which tend to increase the power of the heart's action, and determine a flow of blood to the head. The body should be immediately placed in a recum- bent position, with the head low. The im- pression produced by dashing cold water in the face excites the action of the heart, and often arouses instantly the consciousness. When consciousness returns, an ethereal or alcoholic stimulant may be given, and repose for a time should be enjoined. General cerebral anemia, greater or less in degree, and more or less per- sisting, is referable to various causes, such as compression of the arteries going to the head, valvular lesions of the heart involving obstruc- tion and regurgitation, and feebleness of the heart's action incident to different pathologi- cal conditions. The symptomatic effects are drowsiness, inability to sustain mental efforts, pain in the head, ringing in the ears, and some- times mental hallucinations and illusions. With reference to their effects, it should be added that, as stated under the head of passive conges- tion of the brain, a morbid fulness of the veins within the skull, compensatory for a deficiency of the supply of arterial blood, is inferred from the fact of the contents of the cranium being removed from atmospheric pressure, together with the incompressibility of the cerebral sub- stance ; so that it is not certain how far these effects are due, on the one hand, to anseniia, or, on the other hand, to venous congestion. Par- tial cerebral anasmia, that is, anaemia limited to a portion of the brain, is a morbid condition over which much light has been shed within the past few years by the researches of Kirkes, Vircho w, and others. The arteries of the brain, beyond what is known as the circle of Willis, do not inosculate freely with each other. Hence, if an arterial branch be obstructed, the distribution of blood within the area of the cerebral substance supplied by the obstructed vessel is arrested for a time ; and this defective supply of blood may lead to impaired nutrition, ending sometimes in the loss of vitality or a condition analogous to gangrene. Now, the arterial branches distributing blood to the dif- ferent portions of the brain are liable to be ob- structed, first, by the coagulation of blood with- in them, and second, by a mass of fibrine or a detached vegetation either from the left cavi- ties of the heart or from an artery situated be- tween the heart and the brain. The obstruct- ing substance in the first of these two modes is called a thrombus, and the morbid condition is known as thrombosis; in the second mode the obstructing substance is called an embolus, and the condition embolism ; hence, a thrombus is a stationary, and an embolus a migratory plug. Thrombosis is apt to take place in the vessels within the skull, the coagulation of the fibrine of the blood being due to changes in the arteries which roughen the inner surface of. these vessels. The fibrine is liable to coagulate on a roughened surface over which the blood flows. This is shown by the experiment of in- serting a needle or a thread within a blood ves- sel ; masses of fibrine collect upon the foreign substance. Embolism occurs oftener than thrombosis. Fibrine, a product of thrombosis in the left cavities of the heart, in one of the arteries leading from the heart to the head, or in an aneurismal sac, is liable to bepome separated by the force of the circulating blood, and it is then carried along with the current into the cerebral arteries, until at length it reaches a vessel too small to admit of its pas- sage further onward ; it is thus arrested in its course, and, becoming fixed, it obstructs the circulation in the branches given off beyond the point where it remains. Hence, a partial anse- mia, which is more or less circumscribed ac- cording to the size of the obstructed artery. The same thing occurs when the embolus or plug is a morbid growth or a vegetation, in- stead of a mass of fibrine. Both thrombosis and embolism occur in various parts of the body, as well as within the skull. In the lat- ter situation, the artery most likely to become obstructed, especially by an embolus, is the middle cerebral ; and embolism is far more likely to take place in the left than in the right middle cerebral artery, because the embolus generally comes from the heart, and the most direct route from the latter organ to the brain through the arteries is on the left side. Throm- bosis and embolism give rise to that form of paralysis distinguished as hemiplegia, namely, paralysis affecting the limbs and often the face on one side. The paralysis from embolism occurs suddenly, being a stroke of palsy, because the obstruction occurs suddenly. Often with the sudden palsy there is a temporary loss of con- sciousness, constituting an apoplectic seizure. This is one of several different morbid conditions giving rise to sudden coma or apoplexy. In a certain proportion of cases, the paralysis dis- appears completely after a tune, the circulation being more or less slowly restored beyond the point of the obstruction. Recovery takes place if the circulation be restored before important changes in nutrition have resulted from the de- ficient supply of blood. Softening and even complete loss of vitality of cerebral substance within the space deprived of arterial blood