NERYE-CELLS. 



135 



brown patches caused by gronps of pi-gment granules (fig. 90, b) ; the 

 colour is deeper in adult age than in infoncj. 



The bodies in question are destitute of a proper envelope. The out- 

 runners or branches are formed by prolongations of the same soft sub- 

 stance which forms the cell-body ; they are, therefore, very readily 

 broken, and the cells thereby mutilated, in the manipulation required 

 for their insulation. A fibrillation similar to that in the axis-cylinders 

 of medullated nerve-fibres is seen in these processes (figs. 88, 89) ; it 

 may be observed also passing from them through the body of the cell, 

 and from one process to another ; we have, however, never succeeded in 

 tracing any connection of these fibrils with either the nucleus or the 

 nucleolus of the cell as has been affirmed by some. 



According to Deiters, one process (and only one) of each of the cells 

 of the grey matter of the spinal cord passes directly into the axis- 

 cylinder of a nerve-fibre, as represented in figs. 89, 90. This process he 

 describes as being unbranched from the commencement. The other 

 processes divide into finer and finer branches, but what becomes of the 

 ultimate divisions is not certainly known. The fibrils resulting from 

 the repeated divisions join, it is said, with processes of other cells to 

 form a close network (fig. 90) throughout the grey substance of the 

 cord, and from this network other fibrils may, it is supposed, proceed 

 and unite to form the axis-cylinders of issuing nerves. We may remark, 

 however, that the presence of an undivided axis-cylinder process is by 

 no means so constant in these cells as is commonly described. 



Other cells (fig. 91, a) are found in the nervous substance, 

 which are distinguished chiefly by the pel- 

 lucid, colourless, and homogeneous aspect 

 of the matter contained in them ; such cells 

 possess a nucleus like the rest ; they are 

 seldom large, and have usually a simple 

 round or oval figure, but may also be found 

 branched. They occur along with nerve- 

 cells of the kind before described. Lastly, 

 small bodies of the size of human blood- 

 corpuscles and upwards, containing one or 

 more bright specks like nucleoli, abound in 

 the grey matter in certain situations (fig. 

 91 ^, c.) These bodies, which are some- 

 times called " granules " resemble the nuclei 

 of nerve-cells ; and it may be a question 

 whether they are not the nuclei of cells in 

 which the cell-matter or protoplasm is 

 very scanty, and accidentally detached in 

 examination. These nucleus-like bodies are 

 very abundant in the superficial grey matter 

 of the cerebellum. 



In the grey matter of the cerebro-spinal 

 centre, the nerve-cells appear as if imbedded 

 in a sort of matrix of granular substance, interposed between them 

 in greater or less quantity, and very generally traversed by nerve- 

 fibres. But it is very probable that the appearance of granular 

 or molecular matter results from a confused interlacement of very fine 

 fibrils, and especially of the fine ramifications of nerve-cells ; or from 



Fig. 91. 



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O 



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Fig. 91. — Small Cells from 

 THE Nervous Centres. 



a, from the (cortical) grey 

 matter of the brain, b aud c 

 are from the cortical substance 

 of the cerebellum ; h resemble 

 detached cell-nuclei. c are 

 smaller bodies, also like cell- 

 nuclei, densely aggi-egated 

 (from Hannover, magnified 

 340 diameters). 



