20 
TUMOUR IN THE LATERAL VENTRICLE. 
raena presented by the whole of the lesions spoken of: in a 
word, apoplexy, with a loss of consciousness and voluntary 
motion, more or less complete. Congestion, arising from an 
obstructed return of blood from the head, extravasation of 
blood within the cranium, serous effusion, abscesses, pus, or 
inflammation of the substance of the brain, are all causes of 
apoplexy. The loss of function of any part of the brain 
from the loss of integrity, as in vivisection, and the loss of 
function from torpidity, the result of pressure from effusion 
of blood, or serum, from tumours, or collections of pus, 
differ only, that in the former the loss is immediate and com¬ 
plete, while in the latter it is gradual and more or less in¬ 
complete. 
The s}^mptoms between the mild forms of cerebral lesions 
and the more violent, differ only in degree. They are alike 
in nature, and differ only in force and extent. Now let us 
see how far we are capable of ascertaining the nature and 
the seat of lesions of the encephalon from the phenomena 
during life. I have shown already, that any alteration of 
structure or deposit within the cranium, giving rise to pres¬ 
sure, produces similar phenomena. The decussation of the 
cerebral fibres produces the phenomena of various lesions of 
the brain on the opposite of the body: thus, so far as 
regards the hemispheres, and the sensory and motor bodies 
within the lateral ventricles, loss of function from any cause 
will produce loss of sensibility, defective volition, and im¬ 
perfect vision, on the opposite of the body to that of the dis¬ 
order; but nothing more conclusive, as to the nature or seat 
of the lesion, can be obtained. It is rare that the lesions of 
the encephalon, though they may be gradual in their deve¬ 
lopment, manifest their existence by symptoms of so mild 
and progressive a character as to enable us to judge of their 
nature and seat; but, more commonly, they come on sud¬ 
denly, and with such violence as to deprive the animal all at 
once of sensibility and volition. If the effects of morbid 
lesions of any part of the brain were confined to the part, 
and did not extend to the faculties of other parts of the 
organ, nothing would be more easy than to trace the results 
to their source : but such is not the fact. Pressure upon the 
hemispheres, or within the lobes of the brain of one side, 
will affect, more or less, the whole of it. The incom¬ 
pressible tissue of the brain, and the unyielding nature of 
the cranium, must ensure this in effusions, or the congestion 
attendant upon tumours and abscesses, after irritation is set 
up ; so that it entirely depends upon the degree of pressure 
upon one side of the brain, and the extent of the congestion 
