ATROPHY OF THE BRAIN. 283 



The atrophy occurring after complete development of the brain is 

 sometimes primary, sometimes it accompanies other affections of the 

 brain as a secondary disease. Among the primary atrophies we must 

 first mention that form which occurs as a symptom of senile marasmus. 

 Other senile changes attain unequal grades in different persons, and 

 we also meet very aged individuals who do not show the least sign of 

 cerebral atrophy, while it advances to the highest grade in much 

 younger persons. Next to this comes the atrophy of the brain, which 

 develops in the course of exhausting and consuming diseases. In 

 many cases which are quoted as examples of great resignation and 

 wonderful firmness at the approach of death in tedious diseases, the 

 facts were really badly interpreted ; very often the resignation is cer- 

 tainly due to the dulness and apathy induced by cerebral atrophy. 

 Local diseases of the brain are the chief causes of secondary atrophy. 

 We have already mentioned it as the result of precedent apoplexy, 

 partial necrosis, and partial encephalitis. The paralytic form of idiocy 

 appears to depend on an atrophy of the brain caused by chronic me- 

 ningitis or inflammatory processes in the cortical substance. In other 

 cases the atrophy is the result of continued pressure on the brain. 

 Under this head come the cases where the size of the brain gradually 

 decreases under the pressure of cerebral tumors and hydrocephalic 

 effusions. In meningitis, also, perhaps part of the atrophy is due to 

 the pressure of the inflammatory exudation in the subarachnoid space. 

 Lastly, we must mention that injury and destruction of peripheral 

 nerves occasionally induce secondary atrophy of their centres. 



ANATOMICAL APPEARANCES. When cerebral agenesis is limited 

 to one side, the left is the one generally affected; sometimes the 

 vvhole hemisphere is affected, sometimes only parts of it. In high 

 grades of the disease, the cerebral substance between the ventricles 

 and convex surface has become a thin layer only a few lines thick. The 

 convolutions are scarcely perceptible, or else are very small. The large 

 cerebral ganglia are usually atrophied, and the atrophy extends from 

 them through the crura cerebri to the spinal marrow. The consistence 

 of the atrophic brain is usually increased, its color is somewhat dirty. 

 The space created by the atrophy is filled with fluid that has collected 

 partly in the ventricles, partly between the meninges. The skull is 

 often unsymmetrical, and is thickened at the atrophied part. 



Atrophy of the brain occurring late in life is usually total, but, 

 when it results from partial destruction of the brain, it is generally 

 further advanced on the side corresponding to the disease than on the 

 other. The medulla of the cerebrum is diminished, the convolutions 

 appear thinner, the furrows broader and deeper. The medullary sub- 

 stance is dirty white, more dense and tough, the cortical substance is 



