178 DISEASES OF THE BRAIX. 



ments while the glottis is contracted. In coughing, straining, playing 

 wind-instruments, etc., as we have often shown, the flow of blood into 

 the thorax is hindered ; the pulmonary circulation contains too little, 

 the general circulation too much blood. Under such circumstances, 

 the brain must sufler far more from hyperaemia than other organs sup- 

 plied by the general circulation, particularly the liver, spleen, and 

 kidneys ; because the passage of blood through the upper aperture of 

 the thorax is more impeded than it is through the lower, since these 

 abdominal glands undergo the same compression from the abdominal 

 muscles that the veins of the thorax and the heart do. 



3. We have cerebral congestion in all those diseases of the heart 

 where the function of that organ is impaired, if they are not compli- 

 cated by other anomalies of. opposite effect, and so compensated. In 

 non-compensated valvular disease of the left ventricle, the whole 

 amount of blood in the vessels of the brain and its membranes is not 

 increased, it is true, since, while the veins are overfilled, the arteries 

 are less full ; but the overfilling of the veins obstructs the flow of blood 

 from the capillaries, thus inducing capillary hyperaemia, which, as we 

 have shown, is the most important cause of the cerebral hyperaemia. 

 The affection caused by valvular disease of the right heart is far greater 

 than that from valvular disease of the left heart ; for, in the former 

 case, not only is the escape of venous blood from the brain impeded, 

 but the entire amount of blood in the skull is increased. 



4. The same state of affairs occurs in extensive compression or 

 atrophy of the vessels of the lungs as in pleuritic effusions, emphy- 

 sema, or cirrhosis of the lungs. In these diseases also, when the right 

 ventricle is not hypertrophied in proportion to the impediment to the 

 circulation, the systemic circulation is overloaded at the expense of the 

 pulmonary, and the amount of blood in the skull is increased. Since 

 the contents of the cerebral veins and -sinuses cannot pass into the 

 overfilled jugular veins, the same excessive cyanosis occurs in the brain 

 that is so evident in the skin, and which is almost pathognomonic of 

 the diseases in question. The last stage of emphysema gives us an 

 excellent opportunity of studying the gradual development, steady in- 

 crease, and, finally, the severest symptoms of congestion of the brain. 



Lastly, we must mention a form of cerebral hyperaemia which is 

 neither fluxionary nor congestive, and which is peculiarly important, as 

 it should be very carefully avoided by persons suffering from disease of 

 the blood-vessels, and having a tendency to apoplexy ; I mean those 

 cases of hyperaemia that appear as one symptom of temporary general 

 plethora induced by a very free supply of food and drink. 



ANATOMICAL APPEARANCES. On post-mortem examination, it is 

 often difficult to decide whether the vessels of the cerebral membranes. 



