viii THE HIND-BEAIN 457 



Less convincing from the physiologist's point of view is the 

 larger group of clinical cases of various kinds of tumours in 

 one or other part of the cerebellum, which, in addition to more 

 or less extensive destruction of normal tissue, compress the 

 adjacent organs, beyond the limits of actual disease, particularly 

 the pons and medulla. It is a priori evident that in these 

 cases the fundamental phenomena of cerebral deficiency are 

 masked and to some extent replaced, by irritation or paralytic 

 phenomena, in proportion with the more or less acute course of 

 the disease and the extent and degree of the compression exerted 

 by the tumour on the surrounding parts. 



The mechanical effects of compression are easy to recognise. 

 The crossed hemiplegia and hemiparesis seen in certain cases of 

 tumour of one lateral half of the cerebellum certainly depend on 

 the compression which the tumour exerts on the motor paths in 

 the pyramidal fibres of the same side before they cross. The 

 homolateral paralysis of one or more cerebral nerves by which the 

 syndrome of cerebellar tumours is sometimes complicated is due 

 to the same cause. 



The symptoms which physicians regard, not without reason, as 

 the irritative effects of cerebellar tumours are more frequent, more 

 numerous, and more varied. 



One of the most general is intermittent or continuous headache, 

 which may be localised in the forehead or temples, more often in 

 the occiput, particularly close to that part of the cerebellum which 

 is the seat of the tumour. 



Vertigo in its various forms is another symptom by which the 

 clinical picture of cerebellar tumours is frequently complicated. 

 Some regard it as an essential feature of cerebellar diseases ; the 

 characteristic syndrome of ataxy would thus be only an effect of 

 vertigo. We learn, however, from clinical observation which is 

 in this case of the utmost value since it relates to a subjective 

 phenomenon that ataxy may be present without the faintest sign 

 of vertigo ; that this is almost invariably associated with irritative 

 and compressive lesions of the cerebellum, and is absent in all 

 degenerative and destructive lesions ; finally, that vertigo is not an 

 exclusive symptom of cerebellar diseases, but is very frequently 

 associated with diseases of other parts of the central and peri- 

 pheral nervous systems. 



Vomiting is not uncommonly associated with headache and 

 vertigo, and may depend on the compression of the bulb or 

 on the irritation which spreads to the posterior corpora quadri- 

 gernina, where there is a centre for the contractions of the stomach. 



The forced movements and attitudes by which vertigo is 

 constantly accompanied in animals have usually been observed 

 in clinical cases of compressive and irritative lesions, involving 

 one cerebellar hemisphere. Eotation and circus movements are 



