THE NERVOUS SYSTEM. 789 



arteries from thrombi, emboli, inflammatory changes, spasmodic contrac- 

 tions, etc., or from tumors, exudations, and blood extravasations press- 

 ing upon the vessels from without. In cedema of the meninges, and in 

 the presence of internal hydrocephalus, the brain tissue is apt to be 

 anaemic. The brain tissue in anaemia looks whiter than usual, the con- 

 trast between the gray and the white matter is less marked, and the 

 small blood points usually seen on section from divided vessels may be 

 very inconspicuous or almost entirely absent. 



(EDEMA. 



(Edema of the brain tissue may accompany either general or local- 

 ized hyperaemia, or it may accompany anaemia, and it seems in most cases, 

 though not always, to be dependent upon conditions which induce these 

 alterations in the blood contents of the brain. It is, perhaps, most com- 

 mon in conditions which determine a passive hyperaemia. In some cases 

 of marked impoverishment of the blood a so-called hydrcemic cedema of 

 the brain is found. 



In oedema the brain tissue appears unusually wet and shiny. The 

 same underlying condition is apt to determine an exudation into the 

 membranes and ventricles. There is usually considerable distention of 

 the perivascular lymph-spaces. 



Marked oedema of the brain may exist without brain symptoms. On 

 the other hand, persons may die comatose with no other gross lesion than 

 cedema, either with or without cedema of the pia mater. This is seen 

 with especial frequency in acute and chronic alcohol poisoning, but may 

 occur under other conditions. A careful microscopical examination of 

 the brain under these conditions will frequently reveal structural lesions 

 of more serious import than the oedema. 



Under the designation of "serous apoplexy," cedema of the brain was 

 formerly considered of importance, in the absence of other lesions, as a 

 cause of death. But increased knowledge has led to the general belief 

 that simple cerebral oedema as an independent condition has not the sig- 

 nificance formerly ascribed to it, and it should be accepted, if ever, with 

 great reserve as a cause of death. 



HEMORRHAGE. 



Haemorrhages in the substance of the brain may be very small and punc- 

 tate, and are then usually called capillary haemorrhages ; or they may re- 

 sult in the collection in the brain tissue of masses of blood of consider- 

 able size, which are called apoplectic foci or clots. These forms of 

 haemorrhages may be associated, or a number of capillary haemorrhages 

 may join to form an extensive clot. 



Capillary hcemorrhages may appear, on section of the brain, like the 

 severed ends of hypersemic blood-vessels, or the tissue about them may 



