NERVOUS ACTION. 389 



The nervous system is made up of two elementary struc- 

 tures cells and fibres. " The nerve-cell has been described 

 as consisting of an envelope, granular contents, and a 

 nucleus with one or more nucleoli. So far, there is no* 

 difference between the so-called nerve-cell and any other 

 cell; but it is the great diversity in size, its frequent 

 coloration with pigment, and the brilliancy of a vesicular 

 nucleus which may be regarded as somewhat characteristic 

 of the nervous element, which is usually stellate, round, or 



Fig. 208. Multipolar nerve-cell, showing its nucleus and nucleolus. 



oval, and connected with fibrous prolongations. Some of 

 the cells are as large as -sfath of an inch in diameter, and 

 they are not unfrequently as small as ^-oVo-th. Vesicular 

 bodies are interspersed amongst the cellular elements." 



" The nerve-fibres are found in the nervous centres, and 

 in the nerves which connect the latter with the peripheral 

 parts of the body. They are combined with, or spring 

 from, the nerve-cells in the grey matter of all nervous 

 ganglia. The ultimate nerve-fibres are of two kinds 

 tubular or white and grey or gelatinous. The white have 

 a special envelope, in the interior of which is Bemak's 

 primitive band or axis cylinder (Purkinje), surrounded by a 

 medullary sheath or white substance of Schwann. The 



