352 CHRONIC DISEASES OF THE CEREBRAL STRUCTURES. 



generally, adhesion of the outer to the cranial Avails, and of the 

 inner to the brain-substance, together with a variable amount 

 of a variously organized exudate, either partly fibrillated or in 

 some instances undergoing softening. This alteration of mem- 

 branes and existence of inflammatory exudate may be variously 

 distributed ; often most conspicuous at the base of the brain, 

 involving: the orioin of certain of the cranial nerves, occasion- 

 ally in the sulci, and more rarely in the ventricles. 



h. Slow Changes in Brain-Substance — Cerebral Softening, — The 

 alterations which we encounter in the intimate cerebral struc- 

 tures are chiefly those of change in consistence and colour of 

 circumscribed portions of the mass. This alteration in tex- 

 tural integrity varies from an almost imperceptible softening 

 to a condition of marked diffluence, and in colour from pink 

 to a dirty white. 



The chief causes of this change are probably different grades 

 of inflammatory action, or impairment of nutrition from de- 

 fective blood-supply, following embolism or thrombosis. 



Symptoms. — The indications of either of these conditions in 

 any of their different forms are not, as a rule, attractive or 

 diagnostic. They are rarely connected with excitation or in- 

 tensification of cerebral function, usually with the opposite ; 

 while depending upon the situation and extent of such changes 

 will be the nature and extent of the interference with special 

 function and activities. 



II. Adventitious Growths in Connection with Cerebral 

 Structures. 



Like every other organ, the brain and structures contained 

 within the cranium are liable to become the seat of certain 

 morbid growths or deposits referable to general or constitu- 

 tional causes, or certain local changes, and in consequence of 

 which various of the functions exercised by the encephalic 

 structures are more or less impaired. 



Anatomical Characters. — The chief of these adventitious 

 growths or tumours in the horse are cancer, glioma, cholestea- 

 toma, pa.rasitic and other cysts, and osseous groivths only in- 

 directly connected with the brain. 



Cancer in the soft form, either diffused or as a separate 

 growth, is in rare instances observed in both the membranes 



