796 THE NERVOUS SYSTEM. 



lets of myeliu, nerve cells, shreds of ueuroglia tissue and blood-vessels, 

 and red and white blood cells. The evidence of degeneration is seen 

 in the presence of fat granules and droplets, larger and smaller cells 

 densely crowded with droplets of fat (so-called Gluge's corpuscles or com- 

 pound granular corpuscles}. Various kinds of cells and cell fragments, 

 more or less granular and fatty, and also corpora amylacea, blood pig- 

 ment, fat crystals, and cholesterin crystals, may be found (Fig. 521). 

 The walls of the blood-vessels may also be in a condition of fatty degen- 

 eration (Fig. 522): The color of the softened mass will of course depend 

 upon the relative amounts of these elements. 



The tissue may remain for a long time in the soft condition, or it 

 may be absorbed and replaced by a connective-tissue cicatrix which 

 may be more or less pigmented; or a wall of connective tissue may 

 form about it, converting it into a well- defined cyst, with or without 

 pigmented walls ; or the mass may dry and form a dense, structureless 

 nodule. Acute inflammatory changes may occur about the dead tissue. 

 In cases of infectious emboli numerous abscesses may be formed in addi- 

 tion to their mechanical action. 



Thrombi are most frequent in the internal carotids, less so in the 

 middle_fiie_bral, basilar, and vertebrals,. They may occur, but still less 

 frequently, in other cerebral arteries. Emboli are most common in the 

 middle cerebral artery, next in the internal carotid, and then in the basi- 



FIG. 523. BLOOD-VESSELS FROM AX AREA OF EMBOLIC SOFTENING OF BRAIN. 

 The walls of the vessels, particularly the endothelial cells, contain fat granules and fat droplets. 



lar. The relative frequency with which embolism occurs in the middle 

 cerebral artery is attributable to the directness with which the blood 

 passes into this artery from the heart. The great significance attaching 

 to embolism of the middle cerebral artery is evident when we remember 

 that its branches within the brain jire terminal arteries, and are dis- 

 tributed to such important structures as the lenticular and gaudate nuclei, 

 the internal capsule, and the optic thalaimis. 



Thrombosis and embolism also occur in the vessels of the spinal cord, 



