NERVOUS SYSTEM. (NERVOUS CENTRES. THE MENINGES.) 



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 

 parts to their condition during life. On the other 

 hand, a very advanced stage of decomposition 

 will favour the developement of liquid, wher- 

 ever space 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 anaemia, as in cases where death has 

 terminated a protracted illness, in phthisis 

 for example, or in persons who have died of 

 haemorrhage, 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 any partial atrophy 

 of either brain or spinal cord has occurred, 

 there will invariably be found, at a point cor- 

 responding 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 the 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 

 obserTed where chronic inflammation of the 



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 within 

 the ventricles, that upon the surface is either 

 greatly diminished or entirely disappears. In 

 the ordinary hydrocephalus internus of chil- 

 dren fluid is never found on the exterior of the 

 brain. 



When an arrest in the developement of any 

 portion of the cerebro-spinal axis has taken 

 place, the space which ought to be occupied 

 by the organ of imperfect growth is filled by 

 liquid. In examining the heads of idiots we 

 always find a considerable quantity of sub- 

 arachnoid fluid, either general, or partial if 

 a portion only of the brain be deficient. Or 

 if any portion of the wall of the cranio-spinal 

 cavity be defective, the contained viscus is 

 protected by the accumulation of an increased 

 quantity of liquid in the situation of the de- 

 ficiency. Hence the explanation of those 

 watery tumours which occur over various re- 

 gions of the spine, in cases of spina bifida, in 

 which the accumulation of water is favoured 

 by the absence of the resisting osseous wall of 

 the spine for a greater or less extent. And 

 similar tumours are found projecting from the 

 cranium, being occasioned by a protrusion of 

 the cranial meninges through a congenital aper- 

 ture, containing fluid and sometimes a portion 

 of the encephalon itself. 



Enough has been said to show, that the pre- 

 ternatural increase of this fluid should in 

 general be regarded as secondary to and con- 

 sequent upon the diminished size of the cerebro- 

 spinal centre itself, and that it has most pro- 

 bably little or nothing to do with the manifes- 

 tation of peculiar symptoms during life in the 

 great majority of instances. Whatever be the 

 immediate cause of the shrinking of the cerebro- 

 spinal centre or of any portion of it, the increase 

 of the fluid goes on part passu, and in a 

 quantity duly proportionate to the decrease of its 

 bulk, so that it is in the highest degree impro- 

 bable that, in such cases as I have enumerated, 

 the nervous centre experiences any increased 

 degree of pressure beyond that which it bears in 

 the normal state. If, however, the fluid, either 

 within or without the brain, were to increase, 

 while that organ itself either preserved the 

 same bulk or became enlarged, it is plain that 

 it must experience an increased degree of com- 

 pression, which doubtless would produce se- 

 rious symptoms. This very rarely happens, 

 according to my experience, as regards the 

 subarachnoid fluid on the exterior of the brain : 

 we more frequently meet with an increase of 

 the fluid within the ventricles, and, in such 

 cases, we shall find evidence of the compres- 

 sion in a manifestly greater firmness and 

 density of its structure, and in this fact, that 

 the lateral ventricles, when laid open by a ho- 

 rizontal section, do not collapse, as in the 

 ordinary state of the brain, but remain quite 

 patulous, owing to the firmness and density 

 of their walls. And this patulous state of the 

 ventricles may be regarded as a good indication 

 that the fluid, collected in them, had for 



