214 Oti the Construction of the 



fibres arising there, and to accumulate in considerable masses in 

 the form of wavy loops. Their substance is so delicate as to allow 

 them after a while to adhere to, or apparently fuse with each other, 

 and thus, especially through the action of chromic or acetic acid, to 

 assume the form of a fine network. 



As regards now the nature of these fibrils of the fibrillous layer 

 of the nerve-medulla in general, we can, in considering their general 

 behaviour, hardly come to any other conclusion than that they pro- 

 bably are nervous elements. It could not be well supposed that 

 their formation is due to a coagulation of the nerve-medulla, for 

 they do not appear like fibrin, in the form of an irregular fibrillous, 

 or like albumen, in that of a granulous coagulum, but are always 

 observed to run parallel to each other, either in waves or loops. 

 Acetic acid, which, as is known, causes fibrin as well as the white 

 fibrous tissue to swell, and the walls of cells to disappear, leaves 

 these fibrils unchanged ; on the contrary, they appear in many 

 instances after the treatment of this reagent, only more distinct. 



We will now turn our attention to the most important part of 

 the double-bordered nerve fibre, the so-called axis cylinder. Not 

 many years ago, the pre-existence of this part of the nerve fibre 

 was, as it is known, still disputed, and — probably for the want of a 

 better explanation — it was regarded by some histologists as a pro- 

 duct of coagulation. Additional, more thorough researches, how- 

 ever, not only disproved this view, but further demonstrated that it 

 represented the true nerve fibre. Nevertheless, it was still looked 

 upon as a homogeneous body ; until, some years ago, this view aLso 

 became untenable through Max Schultzes discovery of the fibrillous 

 structure of the axis cylinder. According to the view of this inves- 

 tigator, the axis cylinder consists, as is now generally known, of a 

 number of exceedingly fine and smooth fibrils, which are united into 

 a bundle through an inter-fibrillous, finely granular substance. 

 The conclusion to which I have come from my own examinations, 

 regarding the structure of the axis cylinder, confirms on the whole, 

 it is true, the view just mentioned, but deviates from it in other 

 respects in some essential points. But, notwithstanding, it seems 

 almost that this deviation may possibly be due to a difierence in the 

 mode of examination, as my examinations were, as already stated, 

 principally made with an oblique illumination by means of the 

 achromatic prism. 



According to the results of these investigations, the axis cylin- 

 der consists of minute granules about -j-^VTr ^iiii. in diameter, which 

 are arranged in regular roivs and united by a homogeneous inter- 

 fibrillous substance, and thus form a bundle of gi-anular fibrils. 

 Each axis cyhnder is, therefore, according to its thickness, com- 

 posed of a number of these granular fibrils, which, united into a 

 bundle^ are enclosed within a distinct, delicate memhranous sheath. 



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