STRUCTURE OF NERVE-FIBRES. 33 



the foregoing communication was written, but a copy of 

 which was kindly lent me by Professor Goodsir, soon after 

 Mr. Turner had left Edinburgh for the vacation. According 

 to Stilling, the medullary sheath is, even in perfectly fresh 

 nerves, composed of a network of fibres, which are con- 

 tinuous with others in the axial cylinder and in the proper 

 investing membrane; so that, in his opinion, these three 

 constituents of the nerve-fibre differ from each other only in 

 the manner in which their elements are disposed.* This 

 view is not only quite novel anatomically, but is opposed to 

 the generally received physiological opinion, that the axial 

 cylinder is the essential part of the nerve- fibre, and the 

 medullary sheath an insulating investment. Considering 

 the high estimation in which the writings of Stilling on the 

 anatomy of the nervous centres are deservedly held, and the 

 influence which therefore attaches to his opinions, it seems 

 fortunate that we have been able to present so clear a de- 

 monstration that the axial cylinder is chemically as well as 

 morphologically totally distinct from the medullary sheath. 



With regard to the cause of the fibroid arrangement of 

 the medullary sheath, an observation which I happened to 

 make several years ago, regarding the aggregation of fatty 

 matter, may perhaps tend to throw light upon the subject. 

 I submitted to microscopic examination some of the pulta- 

 ceous slough of a sore affected with hospital gangrene, think- 

 ing it possible that I might discover in it some fungus which 

 might account for the peculiar specific character of that dis- 

 ease ; and found in it numerous bodies, each composed of 

 branching fibres radiating from a common centre, and look- 

 ing, at first sight, like some sort of vegetable growth, so that 

 I made careful sketches of them, one of which is reproduced 

 in fig. 13. But seeing afterwards, in the same object, some 

 bundles of acicular crystals of margarine, having a distant 

 resemblance to the bodies I had drawn, I added ether to the 

 specimen, and found that it dissolved the latter equally with 

 the former. This showed that what first attracted my atten- 

 tion was merely an arborescent form of aggregation of some 

 fat, probably margarine ; and it seems not unlikely that the 

 fluid fat which exists in the medullary sheath of a perfectly 

 fresh nerve, may tend to a similar arrangement of its parti- 

 cles when passing into the solid form, and so give rise to the 

 appearance in question. It is to be remarked that the 

 fibroid character is not peculiar to specimens treated with 

 chromic acid, but also shows itself, though in a less perfect 

 manner, in nerves which have been subjected to other modes 

 * Op. cit., p. 6. 



VOL. Till. D 



