202 DISEASES OF THE NERVOUS SYSTEM. 



eases of the cerebellum, and may also be seen in disease of the 

 pons and the fore ventricles, and, in very rare instances, of the 

 spinal cord. Ataxia occurs very often as a result of distemper, 

 and it occurs without any previous brain or spinal symptoms. 



Concerning disturbances of vision, hearing, and the action of 

 the sphincters, they will be described under their special chapters. 



DISEASES OP THE BRAIN AND ITS COVERINGS. 

 Hypersemia of the Brain. 



Etiology. An active congestion of the brain is caused by an 

 increase of the circulation as the result of increased heart-action. 

 This occurs in hypertrophy of the left ventricle, from excitement, 

 from heat (sunstroke), in great bodily exertion, in teething, and 

 high temperature. 



Passive hypersemia (stagnation) occurs in compression of the 

 jugular veins by tumors, such as large goitres, by obstructed 

 respiration in acute bronchitis, and in compressed conditions of 

 the luugs, extended indurations of the lungs, defects in the venous 

 openings of the heart. Hypersemia of the brain accompanies 

 various acute internal diseases, and as a secondary symptom of a 

 number of disorders; it is also seen as a result of various poisons, 

 such as alcohol, certain narcotics, etc. 



Pathological Anatomy. As a rule, hypersemia of the brain 

 occurs in connection with congestion of the coverings of the brain, 

 especially the pia mater. When hyperaemia is very intense, or 

 where it has existed for a long time, we cannot definitely sepa- 

 rate the conditions. We find the dura mater distended, but very 

 little changed. The vessels of the pia mater are much injected, 

 the torsions of the vessel are flattened, and the sulci are perfectly 

 flat as if pressed out of shape. We find the gray matter is darker 

 red than usual, while the white brain-substance is dull gray or' 

 yellowish-red, and presents numerous bloody spots which may be 

 easily removed. In chronic conditions of this disease we find 

 venous hyperemia. The brain appears in such cases pale and 

 ansemic, very moist and soft, and on section has a brilliant, 

 mirror like lustre. It is lessened in size, and the subarachnoidal 

 fluid is increased. 



