LARGE NERVE-FIBRES. 



425 



A. The envelop, or neurilemma. 



B. Its contents, the neurine; consisting of the medulla and 



the axis-fibre. (Fig. 274.) 



A. The neurilemma? is formed of simple membrane, and resem- 

 bles elastic tissue, but is less soluble in alkalies. Histologically, 

 it very much resembles the myolemma of striated muscular fibre, 

 and has nuclei upon its inner surface (p. 



393, 1). It has not yet been demonstrated in 

 the finest fibres. Moreover, in case of the 

 largest tubes it disappears both at its distal 

 extremity, where it is distributed, and also 

 in the brain or spinal cord, on tracing it to 

 its origin. Sometimes, also, it is wanting 

 even in the coarser fibres through a con- 

 siderable extent of their terminal portions. 



B. The contents of the neurilemma are a 

 homogeneous substance during life, accord- 

 ing to certain observers; and the appear- 

 ances described by Eosenthal and Remak 

 are regarded by such as due to post-mortem 

 changes. The conclusions of Kolliker on 

 this question are adopted here. 



Two entirely distinct substances are con- inner one is the white substance 



J of Schwann (medulla), slightly 



tamed in the nerve-tube; a difference in 

 color, however, and density, being apparent 

 only after death. These are : 



1. The axis-fibre. 



2. The nerve-medulla, or pulp. 



1. The axis-fibre (Kolliker), primitive band (RemaK), or axis-cylin- 

 der (RosenthaT), is a pale, soft, cylindrical or slightly flattened, but 



Nerve-tubes of the common eel. 

 a. In water. The delicate line 

 on its exterior indicates the neu- 

 rilemma ; the dark double-edged 



wrinkled. 6. The same in ether. 

 Several oil-globules have coa- 

 lesced in the interior, and others 

 have accumulated around the ex- 

 terior of the tube. The white sub- 

 stance has in part disappeared. 

 (Magnified 300 diameters.) 



An axis-fibre (c) is seen prolonged some way beyond the broken edge of its neurilemma and the 

 white substance, or medulla (d). 



1 From vg~pov, nerve, and XE^a, a coat or sheath. This term is used to correspond 

 with the myolemma of muscular tissue ; while the perineurium and the perimysium 

 also correspond. 



