154 STRUCTUKE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. 



to recognise distinctly the axis cylinder, with its fibrillar and 

 finely granular structure, within the medullary sheath, as is 

 shown in fig. 21, taken from a fibre from a brain of the torpedo. 

 On this ground I regard the last possible doubt concerning the 

 formerly frequently contested pre-existence of the axis cylinder 

 as entirely set aside. 



The isolation of the axis cylinder is remarkably facilitated 

 by the previous application of fluids which gradually harden 

 albuminous substances, such as dilute solu- 

 tions of chromic acid, bichromate of potash, 

 corrosive sublimate, and others. If these are 

 allowed to act when in a moderate state of 

 concentration, they harden the axis cylinder 

 without any considerable troubling or granular 

 coagulation, whilst the medullary sheath be- 

 comes crumbled and friable. In specimens of 

 such medullated nerve fibres, as, for example, 

 in those from the columns of the spinal cord, the 

 axis cylinders may be either partially or com- 

 pletely isolated from the medullated sheath, 

 for long tracts, with extreme ease ; whilst the 

 peripheric nerves, on account of the resistant 

 sheath of Schwann, furnish preparations of 

 less excellence. In order to see the axis cylin- 

 der in situ, fine transverse sections should be 

 made through a carefully hardened spinal cord 

 or nerve, and this should then be tinted in 

 the ordinary method with carmine. The axis 

 cylinder will now be found to be stained red, 

 whilst the medullary sheath remains uncoloured. The una- 

 voidable shrinking of the soft watery axis cylinder, which 

 occurs when the preparation has been kept in alcohol, causes 

 transverse sections of the reddened axis cylinder to present 

 for the most part a dentated contour line, and to occupy 

 much less space than might be expected from examination 

 made upon fresh nerve fibres. Moreover, in tinted pre- 

 parations, the red axis cylinder may be seen to run longitu- 

 dinally in the unstained medullary sheath, especially if this 

 be rendered transparent by treatment with creosote or oil 



