266 



LECTURE XI. 



FIG. 77. 



Ill 



tissue, which upon the addition of acetic acid, it seen to 

 contain small nuclei, and is different from the looser con- 

 nective tissue which in its 

 turn holds the fasciculi to- 

 gether and constitutes the so- 

 called neurilemma. 



When we use the term 

 nerve-fibre alone in its histo- 

 logical sense, we always mean 

 the primitive fibres, and not 

 ^X^H the fasciculi which to the 



naked eye look like fibres. 



These ultimate fibres in their turn possess, one and all, 

 a special external membrane, which, when it has been 

 entirely freed from its contents a matter certainly very 

 difficult to accomplish, but sometimes occurring sponta- 

 neously in pathological conditions, as for example in cer- 

 tain states of atrophy displays nuclei upon its walls 

 (Fig. 5, c). Within these membranous tubes lie the pro- 

 per nerve-contents, which in ordinary nerves may again 

 be divided into constituents of two descriptions. These 

 can scarcely be distinguished apart in a nerve which is 

 quite fresh ; but in a short time after it has perished or 

 been cut out, or after the action of any medium upon it, 

 they at once separate very distinctly from one another, 

 one of the constituents undergoing a rapid change which 

 has generally been termed coagulation, and by means of 

 which it is marked off from the other constituent (Fig. 

 78). When this has taken place there is distinctly seen 

 in the interior of the nerve-fibre, the so-called axis-cylin- 



Fig. 77. Transverse section through one of the trunks of the brachial plexus. 

 /, /. Neurilemma, from which one thicker partition /' and finer prolongations, indi- 

 cated by light-coloured lines, run through the nerve and divide it into small fasci- 

 culi. These exhibit the dark, punctated, transverse sections of the primitive fibres, 

 and between them is seen the perineurium. 80 diameters. 



