642 
the time which has elapsed since death must 
be taken into account. As advancing decom- 
position favours the transudation of fluids 
through the tissues, it is plain that the longer 
this period is, the less liquid will be found ; and 
the earlier after death the investigation takes 
place, the nearer will be the resemblance of the 
rts to their condition during life. On the other 
d, a very advanced stage of decomposition 
will favour the developement of liquid, wher- 
ever mee may be found for its accumulation. 
It is, therefore, in vain for the pathologist to 
attempt to form an opinion respecting the quan- 
tity of the fluid found in the cranio-spinal 
cavity, unless the inspection have been made 
at an early period after death. 
Practical men are too much in the habit of 
attributing morbid phenomena of the nervous 
system to the influence of the pressure of a 
liquid effusion upon the brain or spinal cord. 
Many facts tend to shew that in a large pro- 
portion of cases, especially in the adult, the 
occurrence of an increased quantity of fluid, 
either around those centres or within the ven- 
tricles, is a result, and that it is probably a 
result of a conservative kind, consequent upon 
a morbid change which depresses the general 
nutrition of those organs themselves. We have 
seen how the universal decay of the tissues, 
which characterizes old age, favours the increase 
of the cranio-spinal liquid, when it affects the 
brain and spinal cord. In examining the 
bodies of habitual drunkards, patients who die 
of delirium tremens, or of cirrhose of the 
liver, the quantity of fluid is always found 
to be considerable and the brain shrunk. In 
bed-ridden persons who have ceased to exer- 
cise their faculties for some time, whether for 
mental or bodily exertion, the same pheno- 
mena are witnessed. When there has been 
much anemia, as in cases where death has 
terminated a protracted illness, in phthisis 
for example, or in persons who have died of 
hemorrhage, or after excessive venesection, 
the nervous centres will be found to be small 
and the liquid in large quantity. In extreme 
cases of lead cachexy, in which the nutri- 
tion of the nervous and muscular tissues is 
materially diminished, I have observed similar 
appearances. And, when an ial atroph 
of either brain or spinal pe igs sentinel 
there will invariably 2 found, at a point cor- 
mwpending to it on the exterior of the organ, 
a local accumulation of fluid occupying a 
depression on its surface which has been 
caused by the giving way of the nervous sub- 
stance within. 
On the other hand an increase in the quan- 
tity of the nervous substance, or an enlarge- 
ment of the brain or spinal cord, consequent 
on an undue injection of their bloodvessels, 
is invariably accompanied with a diminution 
in the quantity of this fluid or with the total ab- 
sence of it. In hypertrophy of the brain no 
fluid is found in oe subarachnoid space, and 
very little or none in the ventricles. In cases of 
tumour of the brain encroaching upon the cra- 
nial cavity, we find no fluid; and the same is 
observed where chronic inflammation of the 
NERVOUS SYSTEM. (Nervous Centres. Tae Menrnces.) 
brain has given rise to a new deposit which 
increases the bulk and the density of the cra- — 
nial contents. In all cases where a considera- 
ble quantity of fluid has accumulated 
the ventricles, that upon the surface is eithe 
greatly diminished or entirely disappears. In 
the ordinary hydrocephalus internus of chil 
- fluid is never found on the exterior of th 
rain. 
When an arrest in the developement of any 
portion of the cerebro-spinal axis has taken 
plete; the space which ought to be occupier 
y the organ of imperfect growth is filled by 
liquid. oe examining the heads of idiots we 
always find a considerable quantity of sub- 
arachnoid fluid, either general, or partial 
a portion only of the brain be deficient. Or 
if any portion of the wall of the cranio-sping 
cavity be defective, the contained viscus is 
protected by the accumulation of an increases 
quantity of liquid in the situation of the de 
ficiency. Hence the explanation of thos 
watery tumours which occur over various 1 
gions of the spine, in cases of spina bifida, } 
which the accumulation of water is 
by the absence of the resisting osseous wall - 
the spine for a greater or less extent. Ami 
similar tumours are found projecting from 1 
cranium, being occasioned by a protrusion - 
the cranial meninges through a congenital ap 
ture, containing fluid and sometimes a por 
of the encephalon itself. - 
Enough has been said to show, that th 
ternatural increase of this fluid should 
general be regarded as to and | 
sequent upon‘the diminished size of the cere 
spinal centre itself, and that it has most p 
bably little or nothing to do with the man 
tation of peculiar symptoms during life in 
great majority of instances. Whatever 
immediate cause of the shrinking of the cers 
spinal centre or of any portion of it, the ine 
of the fluid goes on pari passu, and 
quantity duly proportionate to the decreas 
bulk, so that it is in the highest degree i 
bable that, in such cases as I have enum 
the nervous centre experiences any if 
degree of pressure beyond that which it 
the normal state. If, however, the fluid, 
within or without the brain, were to in 
while that organ itself either preservs 
same bulk or became enlarged, it is p 
it must experience an increased degree ¢ 
pression, which doubtless would pro 
rious symptoms. This very 
according to my experience, as rega 
subarachnoid fluid on the exterior of t 
we more is ag meet with an in 
the fluid within the ventricles, and, 
cases, we shall find evidence of the 
sion in a manifestly greater firmne 
density of its structure, and in this f 
the lateral ventricles, when laid open 
rizontal section, do not collapse, a8 
ordinary state of the brain, but re 
patulous, owing to the firmness 
of their walls. And this patulous state 
ventricles may be ed as a gooG 1D 
that the fluid, collected in them, 
