THE NERVOUS SYSTEM. 401 



measuring in the cord, 0-0022, in the brain 0-002 of a line. Of the 

 veins, the largest, for the most part, do not present a trace of smooth 

 muscle, exhibiting nothing but connective tissue with nuclei, or fine 

 elastic filaments and epithelium ; in the smaller ones I have, occasion- 

 ally, though very rarely, observed contractile elements. 



In the ventricles of the brain there exists, under normal conditions, 

 an extremely small quantity of clear serous fluid, which is manifestly 

 secreted by the arterial plexuses, and which, probably aided by the 

 ciliary movements, assists in the nutrition of the walls of the cavities. 

 A second fluid, the liquor cerebro-spinalis is contained in the suba- 

 rachnoid spaces above described, which according to Luschka, are lined 

 by an epithelium, and from the largest of which, extending from the 

 base of the brain to the termination of the canal of the dura mater 

 mcdullce, the fluid in question may be readily obtained. It is alkaline, 

 contains of water 98-56 albumen and extractive matter 0-55 salts 

 0-84 per cent., principally chloride of sodium. Its principal function 

 appears to be to conduce to the more free motion of the central nervous 

 system, and to act as a regulator in varying degrees of fulness of the 

 vascular system. 



A few pathological points may here be referred to. The ependyma 

 ventriculorum presents not only, as above mentioned, almost constantly 

 in places, a thin fibrous substratum, but is frequently, especially in 

 dropsy of the ventricles, and in old age, very much thickened by a 

 layer of that kind. In either case it invariably contains, as was first 

 mentioned by Purkinje, yellowish bodies, with con- 

 centric striae of a round or biscuit shape, and not 

 unlike starch granules. They are scarcely affected 

 by acids, whilst in caustic alkali they become pale 

 and gradually dissolve. I find these corpuscula 

 amylacea (Fig. 153), almost always on the fornix, 

 the stria cornea, and septum pellucidum, and also 

 elsewhere in the walls of the ventricles, as well as 

 in the cortical substance of the brain, in the medul- 

 lary substance of the cord, and in the filum termi- 

 nate ; in the first-mentioned situations they frequently 

 occur in incredible quantity, close together, in the 

 newly formed connective tissue, or between the ner- 

 vous elements. That these bodies are a pathological 

 product is certain, but not so of what they consist, 

 or how they are formed, although everything indicates a nitrogenous 



Fia. 153. 1, " Brain-sand'' from the pineal gland, in bundles of connective tissue: 2 f 

 corpuscula amylacea from the ependyma of Man ; magnified 350 diameters. 



26 



