82 TISSUES OF THE NERVOUS SYSTEM. 



whether in the fresh state or treated with gold, in the cornea 

 of the frog or of mammalia treated with gold, in sections of 

 the epiglottis or of the mucous membrane of the mouth made 

 after treating the tissue with gold the Schwann's sheath can 

 be often recognized as a more or less distinctly streaked mem- 

 brane. It generally ceases where the non-raedullated fibres 

 split into their constituent fibrils. 



Non-medullated Fibres. Various methods must be 

 used for the demonstration of the non-medullated fibres, for 

 the same method does not answer equally well in all cases. 

 Among these, chloride of gold has, unquestionably, the first 

 place. In very many instances it affords the only means we 

 have of following these fibres to their finest ramifications, e. g., 

 in the skin, mucosa, cornea, and striped muscular tissue, etc. 

 Osmic acid is also very useful. The silver method, or treat- 

 ment with certain acetic acid mixtures, is occasionally em- 

 ployed. In membranes which are prepared in the fresh state 

 in an indifferent liquid, individual non-medullated nerve fibres 

 can be seen, but their finer ramifications cannot be traced, even 

 in the most transparent, without the aid of the reagents above 

 mentioned. 



SECTION II. NEBVE CELLS. 



Nerve Cells, i.e., ganglion cells, may be investigated (a) 

 in the ganglia which are attached to the spinal and certain 

 cerebral nerves ; (6) in the gray substance of the brain and 

 spinal cord ; (c) in ganglia belonging to the sympathetic 

 system. 



(a) Ganglia of the Cranial and Spinal Nerves. As 

 may be seen in sections of these ganglia (hardened in chromic 

 acid or Miiller's fluid), each of them is inclosed in a capsule. 

 This capsule varies in thickness in different ganglia, and is 

 continuous with the neurilemma of the nerves which enter and 

 leave the ganglion. It consists of fibrillated connective tissue, 

 in which the cellular elements proper to that tissue may be 

 distinguished. From it septa of connective tissue stretch in- 

 wards, and unite by anastomosis so as to form a meshwork. 

 This meshwork serves to support the rich vascular system with 

 which the ganglion is provided. Its meshes arc occupied by 

 the nerve fibres and by ganglion cells. These last consist of a 

 substance partly granulous, partly fibrillated, in which a 

 vesiculated, spheroidal, sometimes oblong, nucleus is em- 

 bedded, which itself incloses a shining nucleolus, the position 

 of which may be either central or eccentric. 



For the study of these cells, teased preparations must be 

 used. The spinal ganglia of fish, particularly of the roach 

 and pike, the Gasserian ganglion of the frog, or the ganglion 



