STRUCTURE OF NERVE-FIBRES 103 
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 pultaceous 
slough of a sore affected with hospital gangrene, thinking it possible that I might 
discover in it some fungus which might account for the peculiar specific character 
of that disease; and found in it numerous bodies, each composed of branching 
fibres radiating from a common centre, and looking, 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, J added ether to the specimen, and found that it dissolved 
the latter equally with the former. This showed that what first attracted my 
attention 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 particles when passing into the solid form, and so give rise to the appear- 
ance 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 of prepara- 
tion—for example, after exposure for a few seconds to a temperature of 212° Fahr. 
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 connect 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 con- 
tinuous, 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 connective tissue are much more delicate than the constituents of the 
medullary sheath, which are often comparatively coarse, as may be seen from 
Fig.11r. In the columnar regions of the cord, the former require a high magnify- 
ing power to be applied to very thin sections, in order to distinguish 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 con- 
nective tissue. 
Op xcit.. Pugs 
