180 PRACTICAL MICROSCOPY. 



THE NERVOUS SYSTEM, 



STRUCTURAL ELEMENTS. 



The elements of the nervous system are : 



1. Nerve Fibres. 



2. Nerve Cells. 



3. Connective Tissue. 



4. Peripheral Termini. 



i 



NERVE FIBRES. 



A typical nerve fibre consists of three portions, viz.: a central 

 conducting portion, the axis cylinder ; the medullary sheath, or 

 white substance of Scliwann ; and the enveloping connective-tissue 

 substance, the neurilemma. This constitutes a medullated nerve- 

 fibre, and is found largely in the trunks of the cerebro-spinal 



FIG. 118. SEPARATED NERVE FIBRES. X 400. 



A. Neurilemma of a fibre. 



B. White substance of Schwann, stained with osmic acid, which hides the axis cylinder. 



C. Nucleus of the neurilemma. 



D. One of Ranvier's nodes in an osmic acid stained fibre showing the axis cylinder between 

 the separated portions of Schwann's sheath. 



E. A medullated fibre, teased in normal salt solution. The medullary substance has be- 

 come coagulated on exposure and removal. The axis cylinder is faintly seen. 



F. Axis cylinder at torn extremity. 



G. Non-medullated fibre. 



H. Fibres without neurilemma. Small clusters of medullated substance are seen covering 

 the axis at irregular intervals. 



