662 



A MANUAL OF PHYSIOLOGY 



the ground substance between the fibrils lie round, angular, or 

 spindle-shaped bodies (Nissl's bodies) which stain with basic dyes 

 (Fig. 235).* These bodies vary in appearance in different kinds of 

 nerve-cells, and in the same nerve-cell under different conditions. 

 In a multipolar cell, like those in the anterior horn of the spinal cord, 

 several processes it may be five or six, or even more pass off from 

 the cell-body. The most complete pictures of them are given by 



preparations impregnated ac- 

 cording to the method of 

 Golgif (Figs. 227, 229). 

 One of the processes 

 is distinguished from the 

 rest by the fact that it 

 maintains its original dia- 

 meter for a comparatively 

 great distance from the cell, 

 and gives off comparatively 

 few branches. This process, 

 which in favourable prepara- 

 tions can be traced on till it 

 becomes the axis-cylinder of 

 a nerve-fibre, is called the 

 axis-cylinder process, or more 

 shortly the axon. The few 

 slender branches that come 

 off from it, usually at right 

 angles, are called collaterals. 

 Both the main thread of the 

 axon and the collaterals end 

 by breaking up into an arbor- 

 escent system of fibrils or 

 telodendrion. The teloden- 

 drions vary greatly in appear- 

 ance from simple end-brushes 

 FIG. 228. LARGE PYRAMIDAL CELL OF to far-branching thickets, or 

 CEREBRAL CORTEX (BARKER, AFTER BECH- such special end-organs as 

 TEREW). motor-plates (Fig. 231) or 



a, axon ; b, dendrite. muscular spindles (Fig. 329). 



The rest of the pro- 

 cesses of the cell, which are termed dendrites or protoplasmic 

 processes, very rapidly diminish in diameter, as they pass away 

 from the cell, by breaking up into fibrils like the branches of a tree. 

 The Nissl bodies extend for some distance into the dendrites, but not 

 into the axon. The dendrites of some cells, especially the pyramidal 



* In Nissl's method the sections are stained in a solution of methylene 

 blue, and decolourized in anilin-alcohol. 



f The method depends upon the deposition of mercury, or silver, in or 

 around the cell-bodies and their processes in tissues which have been 

 hardened in bichromate of potassium and then soaked in a solution of 

 mercuric chloride or silver nitrate. In Pal's improvement of Golgi's 

 method a solution of sodic sulphide follows the mercuric chloride. 



