NERVES. 



561 



Fig. 300. ,4 stel- 

 late nerve-corpus- 



and before unaccountable state of the surface known as 

 goose-skin. 



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 transverse mark- 

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

 consistent, of a reddish grey colour, and 

 generally fiat. 



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, o^, which at a is 



* , .. j filled with a cor- 



transparent, structureless tissue surrounds p usc ie containing 



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 ; it therefore becomes 



necessary to exercise considerable care in ken r: from* the 



breaking up structures to view these tubules, root of a spinal 



which should be immersed in a very weak nerve< 



solution of spirit and water. Mr. Lockhart Clarke, while 



engaged in his researches on the minute structure of the 



spinal cord, placed the cord, immediately after removal, 



into strong spirits of wine. 



This, he found, hardened it, 



and he was thus enabled to 



make very thin sections. As 



nerves approach the brain or 



spinal cord, they gradually 



become smaller, measuring 



l-10,000th to l-14,000th of 



an inch in diameter. The dif- Fig. SOL Termination of nerve loops 



ference in the nerve substances 



is not an affair of colour only; it refers also to their 



intimate structure and organisation : the white matter is 



made up of bundles of tubular fibres, the grey is composed 



o o 



puscles with nu- 

 clei and their nu- 

 cleoli: at ft is a 

 corpuscle enclos- 

 ing within its 

 sheath granular 



