720F NERVOUS SYSTEM. (NERVOUS CENTRES. ABNORMAL ANATOMY.) 



quantity from half an ounce to several ounces. 

 Sometimes it is milky, and has shreds of lymph 

 floating in it; at other times it may be sero- 

 purulent, but this is extremely rare, and only 

 occurs when the lining membrane has been the 

 seat of acute inflammation and of inflammatory 

 deposit. 



The lining membrane of the ventricles, which 

 in health is of extreme tenuity, becomes fre- 

 quently thickened and partially opaque in chro- 

 nic disease of the brain, where the ventricles 

 are more or less dilated. In acute disease 

 lymph is sometimes deposited upon it in large 

 and loose flakes, easily removeable from it. 

 And sometimes there is a deposit all over its 

 surface of a fine granular semitransparent 

 lymph, which gives to the internal surface of 

 the membrane the appearance of an extremelv 

 fine and delicate reticulation. 



As the choroid plexus are covered by a pro- 

 longation of the membrane of the ventricles, 

 their investment is apt to participate in any 

 morbid process which may take place in the 

 former. In acute affections it will be covered 

 with lymph, as the membrane lining the ven- 

 tricles is elsewhere. When much water has 

 been accumulated in the ventricles, the choroid 

 plexus are pushed against their floor, flattened, 

 and rendered pale by maceration. On the other 

 hand, whatever causes much vascular congestion 

 in the vessels of the brain will produce the same 

 effect in a marked manner upon those of the 

 choroid plexus. 



Earthy concretions are sometimes found in 

 the choroid plexus, which may probably be an 

 augmentation of the crystalline matter found in 

 them in their healthy state. These appear to 

 consist chiefly of phosphate and carbonate of 

 lime. 



A very common appearance found in the 

 choroid plexus consists in certain vesicles, very 

 variable both in size and number. These are 

 simple cysts, containing a straw-coloured fluid. 

 Formerly they used to be regarded as hydatids, 

 but they are now known to be essentially dis- 

 tinct from them. They occur frequently in 

 brains which exhibit no other departure from 

 the normal condition. Of their precise nature, 

 and of their cause and mode of formation, 

 nothing is known ; and as they are seldom of 

 a large size they are not likely so to disturb 

 the functions of the brain as to give rise to 

 symptoms by which their presence could be 

 detected. 



On the pseudo-morbid appearances of the 

 nervous centres and their coverings. The ac- 

 tual indications afforded by any departure from 

 the normal physical condition of the nervous 

 centres after death are so important to the attain- 

 ment of right conclusions respecting the patho- 

 logy of the nervous system, that it behoves the 

 anatomist to take fully into account all those 

 circumstances which may give rise to appear- 

 ances in the cerebro-spmal centres or their 

 membranes simulating disease. Such appear- 

 ances, not inappropriately termed pseudo-mor- 

 bid, occur in the greater or less vascular fulness 

 of the membranes and of the centres themselves, 

 in the variations in the quantity of fluid around 



or within the brain, or around the spinal cord, 

 and in the consistence of the nervous matter. 



The circumstances which affect the amount 

 of blood in the vessels are the mode of death 

 and the position in which the head has been 

 laid after death. Death by asphyxia, whether 

 rapid or gradual, favours the accumulation of 

 blood in the vessels of the brain. Convulsions 

 preceding death likewise cause turgescence of 

 these vessels. Any impediment to the circula- 

 tion through the heart has the same effect, but 

 to the greatest degree when the impediment is 

 much felt on the right side of the heart. 



The position of the head after death affects 

 the vascular fulness by favouring the accumula- 

 tion of blood in the most dependent parts. 

 From this circumstance and from the custom 

 of placing bodies on the back, we always find 

 the posterior lobes of the cerebral hemispheres 

 and the cerebellum most filled with blood, and 

 it is on this account that the straight and other 

 posterior sinuses of the dura mater are always 

 filled with blood. 



The quantity of fluid around the brain and 

 spinal cord is least in the young and greatest in 

 the old : it is influenced by the bulk of the 

 brain or spinal cord, sometimes disappearing 

 entirely when the brain is so large as to fill the 

 cranial cavity; it is inversely as the quantity of 

 blood, and therefore is considerable in cases 

 of anaemic brain, unless the bulk of the organ 

 have increased from some other cause. Slow 

 deaths from chronic disease favour the accu- 

 mulation of this fluid by diminishing the supply 

 of blood to the brain. In phthisis and other 

 lingering maladies there is almost always a con- 

 siderable amount of subarachnoid fluid. The 

 practitioner should bear in mind that the ab- 

 sence, of subarachnoid fluid is always abnormal, 

 and is in general due to an enlargement of the 

 brain from hypersemiaor from some other cause. 



Softening of the nervous matter may be 

 pseudo-morbid. The spinal cord softens very 

 soon after death ; but if examined within 

 twenty-four hours it exhibits more density than 

 the brain. With the advance of decomposition 

 the cord becomes extremelv soft and almost 

 diffluent. In the brain the pseudo-morbid 

 softening is colourless, and may be readily 

 mistaken for disease. That the brain is very 

 prone to imbibe fluids is shown by Dr. Patter- 

 son's experiments. The brains of sheep were 

 allowed to remain for a certain number of 

 hours in a given quantity of water, which was 

 rapidly absorbed. The weight of the brains 

 was increased proportionally to the quantity of 

 water which had been imbibed, and the parts 

 most exposed to the fluid were found in a soft- 

 ened state. In one instance the brain was de- 

 prived of its membranes on one side, and six 

 hours after death it was immersed in a mixture 

 composed of equal parts of ox-bile and water. 

 It weighed three ounces, seven drams, and four 

 grains when prepared for experiment. After 

 remaining in the mixture thirty-six hours it 

 weighed eight ounces and one dram.* These 



* On the pseudo-morbid appearances of the 

 brain, Ed. Mcd. ;md Surg. Journ. for 1842, 

 vol. 57. 



