THE NERVOUS SYSTEM. 399 



axis-cylinder is unchanged, even when boiled, in which case it 

 is readily isolated and appears somewhat contracted ; by ether 

 and alcohol it is undissolved even by boiling;, but shrinks to 

 some extent. The latter effect is produced also by corrosive 

 sublimate, chromic acid, iodine, and carbonate of potass. 

 Viewing all these reactions together, it might perhaps be stated 

 with certainty, that the axis cylinder is a coagulated protein 

 compound which, however, differs from fibrin, inasmuch as it 

 is insoluble in carbonate of potass and solution of nitre, and 

 offers much greater resistance to acetic acid and caustic alkalies. 

 On the other hand, it agrees with the substance of which the 

 muscular fibres are composed, in its elasticity and insolubility 

 in carbonate of potass, differing from it in its insolubility 

 in dilute hydrochloric acid, and difficult solubility in acetic 

 acid. 



These are the most important facts connected with the axis- 

 cylinder. The conclusion which may be drawn from them, 

 appears to me, to be simply this, that the axis-cylinder is not 

 an artificial product, but that it must be regarded as an essential 

 constituent of the living nerves. The only objection which can 

 be urged against this opinion consists in the circumstance, that 

 the axis-fibre cannot be seen in living fresh nerves, and that it 

 cannot generally be distinguished, as a special structure, in the 

 interior of the nerve-tubes without the aid of reagents. But it 

 must be remarked that it can also be bronylit into raw in nerves 

 that are still warm. Thus I find well-marked projecting axis-fibres 

 at the roots of the cerebral nerves in Frogs just killed, which 

 I have examined as quickly as possible, after the application of 

 a solution of sugar, particularly in those of the optic, trigeminal, 

 and vagus, also in the spinal nerves, for instance in the second. 

 I see them under the same conditions in the peripheral nerves 

 of the Frog that have been teased out, and, in these nerves, have 

 on several occasions, even distinctly noticed the axis-fibres in 

 the form of convoluted filaments, in larger drops of the nerve- 

 pulp expressed from the tubes (fig. 137, 2). The only fact, 

 therefore, that can be adduced in opposition, is this, that it is 

 quite true that the axis-fibre cannot, with certainty, be perceived 

 in the interior of the recent nerve-tubes themselves, except upon 

 the application of some reagent ; but this circumstance obviously 

 proves nothing at all, because neither can it be seen in the interior 



