34 ON THE STRUCTURE OF NERVE-FIBRES. 



of preparation — for example, after exposure for a few seconds 

 to a temperature of 212° F. 



There is another important statement made by Stilling, 

 which the use of the method of examination above described 

 enables me to correct. He speaks of the fibres which con- 

 nect one nerve- fibre with another as similar in every respect 

 to those seen in the medullary sheath.* I find, however, 

 that both in the sciatic nerve and in the spinal cord of the 

 cat, the connective tissue between the nerve-fibres, like the 

 neurilemma and pia mater, with which it is continuous, 

 becomes coloured by the carmine; whereas, the medullary 

 sheath, as before stated, is quite unaffected by it, proving 

 that the two structures are chemically distinct from one 

 another. In both these situations, too, the fibres of the con- 

 nective tissue are much more delicate than the constituents 

 of the medullary sheath, which are often comparatively 

 coarse, as may be seen from fig. 11. In the columnar re- 

 gions of the cord, the former require a high magnifying 

 power to be applied to very thin sections, in order to distin- 

 guish them, and are often present in such extremely small 

 quantity that, without very careful examination, the nerve- 

 fibres appear actually in contact with one another. In the 

 sciatic nerve I have observed occasional elongated nuclei in 

 the connective tissue. 



I may add that glycerine has proved very useful, not only 

 for permanently preserving the preparations in the moist 

 state, but also as an aid to investigation ; for it renders the 

 sections much more transparent, without making the white 

 substance of Schwann invisible, as turpentine does; and 

 hence the course of the nerve-fibres through the cord can be 

 traced much more easily, and, at the same time, the propor- 

 tion between the medullary sheath and axial cylinder can be 

 readily ascertained. Thus, by examining transverse sections 

 of the cord in this way, I find that while Kolliker is quite 

 correct in his statement that the fibres of the roots of the 

 nerves diminish in size in passing inwards through the 

 columnar regions,t yet the diminution affects only the white 

 substance ; the axial cylinder often retaining its full dimen- 

 sions even in the middle of the gray matter, while the medul- 

 lary sheath is reduced to a very thin crust, so that the nerve- 

 fibre assumes a character differing but little from that of an 

 offset of a nerve-cell. 



* Op. cit., |>. 7. 



f Kollikoi's 'Handbuch der Gewebelehre,' 3d edit., p. 835. 



