NERVOUS STRUCTURE. 



699: 



and before unaccountable state of the surface known as 



n. 



Nerves. The nervous system consists of 

 brain, spinal marrow, and nerves. There 

 are two sets of nerves in the body ; in the 

 one set the nerves are white, firm, shining, 

 more or less rounded, with trans verse mark- 

 ings ; in the other, they are softer, not so 

 consistent, of a reddish grey colour, and 

 generally flat. 



Under the microscope, nerves are seen to 

 be composed of minute fibres or tubules, full 

 of nervous matter, arranged in bundles, 

 and connected by an intervening fibro-cel- 

 lular tissue, through which capillaries ramify. 

 A layer of the same, or of a more delicate, 

 transparent, structureless tissue surrounds 

 the whole nerve, forming a sheath. The 

 slight pressure of the thin glass, when 

 placed on the nerve-fibre, causes nearly the 

 whole of the contents to flow out in the 

 form of a granular material j it therefore 

 becomes necessary to exercise considerable 

 care in breaking up structures to view these 

 tubules, which should be immersed in a 

 very weak solution of spirit and water. 



On Microscopical Examination of Nerves It would 

 scarcely be necessary to insist on the great importance of 

 removing and examining the 

 nervous centres as soon as 

 possible after death, were it 

 not that the practice is too 

 often neglected. Great cau- 

 tion also should be exercised 

 to avoid injuring the parts, so 

 that when hardened, perfect 

 or entire sections of them may 

 be obtained for examination 

 under the microscope. After they have been carefully 

 examined externally, by the assistance of a lens, if neces- 

 sary, incisions should be made, not at random, but in a 



330. A Stel- 

 late nerve corpus- 

 cle, with tubular 

 processes issuing 

 out, which at a 

 is filled with a 

 corpuscle con- 

 taining black 

 pigment, above 

 this are corpus- 

 cles with nuclei 

 and their nu- 

 cleoli ; at 6 is a 

 corpuscle en- 

 closing within 

 its sheath gra- 

 nular matter : 

 this is taken, 

 from the root of 

 a spinal nerve. 



3Bl ,_ Termination of nerve . loop , 

 in muscles. 



