Physiology of Nerves and Nerve-cells. 503 



cells have processes or branches of the same matter as the cell ; that is, 

 finely granulated protoplasm. These processes become finer as they go 

 from the cells, and branch out into several parts, and the parts from 

 neighboring cells mingle with each other and connect the different cells 



FIG. 237. 



(Rosenthal.) 



FIG. 237 .Ganglion cells from Human Brain. 



1. A ganglion cell of which one process (a) becomes the axis cylinder of a nerve fibre (6). 

 2. Two cells, a and b, interconnected. 



3. Diagrammatic representation of three connected cells, each of which passes into a 

 nerve fibre. 4. Ganglion cell partly filled with pigment. 



together. But from each cell one or more fibres are sent out, 

 which, at a little distance from the cell, becomes encased in a medullary 

 sheath, and thenceforth becomes, in appearance and probably in fact, a 



FIG. 238.-Nerve Cells. 



?. Bipolar Ganglion Cell. 

 .Nerve cell from anterior horn of 

 human Spinal Cord. 

 p. Pigment body. ( Gerlach.) 



peripheral nerve fibre, or a con- 

 ductor to another cell. The pe- 

 ripheral nerves are simply con- 

 ductors of the nerve electric 

 fluid or movement. The cen- 

 tral system is the medium of 

 all motion and sensation. If 

 one of the nerves connecting 

 the central system, and a mus- 

 cle be irritated, it will cause 

 pain and also a contraction of 

 the connected muscle. If the 

 nerve is cut above the point at 

 which it is irritated, the muscle 

 FIG. 238. below will still contract upon 



the irritation of the nerve, but the sensation of the pain will be gone. 



But if the nerve is cut below the point of irritation aforesaid, the pain 



