272 LECTURE XI. 



quently displays itself in this way, that when a nerve is 

 torn across or cut (Fig. 78, m, m\ the medulla usually 

 protrudes from it, presenting, especially after it has been 

 acted upon by water, a peculiar striated appearance (Fig. 

 80, A). It takes up water namely, which is a proof that 

 it is not a neutral fatty substance in the ordinary sense 

 of the term, but can at most, on account of its great 

 power of swelling up, be compared to certain saponace- 

 ous compounds. The longer the action of the water lasts, 

 the longer are the masses which protrude from the nerve. 

 They have a peculiar, ribbon-like appearance, keep con- 

 tinually acquiring new streaks and layers, and give rise 

 to the most singular shapes. Frequently also fragments 

 become detached and swim about, forming peculiar, stra- 

 tified bodies, which in recent times have been confounded 

 with corpora amylacea, but are distinguished 

 FIG. si. f rom them in the most positive manner by their 

 a b _ e chemical reactions. 



With regard to the histological varieties of 

 nerves amongst themselves, investigation shows 

 that in different parts more or less highly deve- 

 loped forms greatly predominate. On the one 

 hand, namely, the nerves are essentially distin- 

 guished by the breadth of their primitive fibres, 

 on the other hand, by the presence of medulla. 

 We have very broad, middle-sized and small 

 white fibres, and in like manner broad and fine 

 grey fibres. A very considerable size is generally speaking 

 but seldom attained by the grey ones, because the size 

 of a nerve depends more uporl the greater or less quan- 

 tity of medulla it contains than upon the volume of the 

 axis-cylinder, but still variations present themselves 



Fig. 81. Broad and narrow nerve-fibres from the crural nerve with the medullary 

 substance irregularly swollen up. 800 diameters. 



