160 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. 



an interfibrillar substance. For this investigation I especially em- 

 ploy the lateral columns of the spinal cord with their thick medul- 

 lated fibres, from which, on account of the absence of the sheath of 

 Schwann, it is easy to isolate the axis cylinder, not only when quite 

 fresh, with the addition only of a little serum, but still better after 

 twenty-four hours' or more maceration in solution of iodine in serum, 

 in which the axis cylinder becomes slightly hardened without shrink- 

 ing or otherwise materially altering in appearance. Perosmic acid 

 is also here of great service, solutions of which, varying in strength 

 from one-half to one-eighth per cent., acting for a short time on the 

 axis cylinder, harden it without materially changing its volume, and 

 without producing a trace of granular coagulation. Axis cylinders 

 thus freed from the medullary sheath show with remarkable distinct- 

 ness the characters of parallel striation. But even whilst still con- 

 tained within the medullary sheath, the fibrous and granular structure 

 of the axis cylinder may be observed, as I was first convinced from 

 observations made on the thick fibres of the brain of the torpedo, 

 which possesses a proportionately thin medullary sheath.* 



A decisive argument in favour of the fibrillar structure of the 

 axis cylinder is derived from the observation of its origin from 

 the great nerve cells of the spinal cord or of the brain. In regard 

 to this point I must refer to the following account, and to the essay 

 I have just cited, in which the particular observations are given, and 

 will only mention here that the fibrils which emerge in a convergent 

 direction from the cell substance, in order to form the axis cylinder pro- 

 cess of the cells, unite, and are often far removed from one another 

 by interfibrillar material (see figs. 18, 29, and 30, at a.) The forma- 

 tion of the proper axis cylinder results from a diminution in the 

 quantity of the interfibrillar material, whilst the fibrils become more 

 closely approximated in their parallel course, so that ultimately only 

 a very small quantity of interfibrillar substance remains. In the 

 periphery also it is not difficult to see the fibrillar character of soli- 

 tary axis cylinders, as, for example, in the corpuscles of Yater and 

 Pacini, as was shown to me by Dr. Grandry, providing the specimens 

 are examined in the perfectly fresh state, without other addition than 

 that of serum, and with sufficiently high powers. 



I consider it, indeed, to be possible that, notwithstanding these 



* See my Essay, entitled Observations de cellularum, Jibrarumque 

 nervearum Structura, Banner Universitdts Programm, 1868, fig. 5, and the 

 preceding woodcut, 21, p. 154. 



