CEREBRAL TUMOURS. 495 



brain there are occasionally deposits, especially in very- 

 young animals, and connected with a tubercular diathesis. 

 This disease has been termed tubercular meningitis, and is 

 by no means so well marked or frequent in the lower 

 animals as in man. 



Melanotic deposits and fibrous tumours occasionally occur, 

 but are not usually of such a size in connection with the 

 meninges as to lead to serious symptoms. 



CEREBRAL TUMOURS. 



In the brain the tumours which most commonly occur in 

 horses are those of the choroid plexuses. These occur rather 

 frequently in lowbred carriage-horses, and usually appear on 

 both plexuses at once, and consist in abnormal accumula- 

 tions of cholesterine, a non-saponifiable fat which occurs 

 in rectangular scales. This cholesterine, with serum and 

 amyloid or starch-like bodies, is found at first in the hyper- 

 trophied villi of the plexuses. In most old horses there 

 is more or less enlargement of these vascular structures, 

 but in some the growths acquire the characters of true 

 cholesteatomatous tumours that is to say, tumours con- 

 sisting almost entirely of cholesterine, which is found packed 

 in spherical masses, and these are surrounded by a some- 

 what dense capsule. The connective tissue in the substance 

 of the tumours is scanty. 



These tumours of the choroid plexuses grow slowly, and 

 do not therefore induce severe symptoms until they have 

 perhaps attained the size of a pigeon's egg. I have met 

 with them as large as a hen's egg. They then usually give 

 rise to staggering symptoms, which come on with great 

 severity at intervals. When the fits are not on, the animal 

 may appear quite healthy, fat, and in good working order ; 

 but under the influence of generous diet and work, violent 



