Dark or Double-hordered Nerve Fibre. 211 



about xitf iiini. In the interior of the fibre they appear in a hexa- 

 gonal form, but after they have made their escape through its open 

 ends, they resume their original round form. These apparent 

 vesicles or cells probably consist of certain fat-Uke constituents of 

 the medullary layer, and are formed during the separation of the 

 dififerent bodies of which it is composed. They are especially met 

 with in the nerve fibres of man, of the ox, or of such animals, where 

 opportunity of examining them immediately after death is wanting, 

 for which reason they may also be regarded as a product of a natural 

 decomposition. Treated with ether, they are seen to dissolve within 

 the fibre, or, assuming a round form, to travel toward its open end. 

 When fresh nerve fibres, after having remained for some hours in 

 ether, are examined, their fat-like constituents will be found to have 

 almost entirely disappeared, and, besides a number of fibrils, the 

 remains of the albuminous constituents are only met with in the 

 form of coagulated molecules or small irregularly-shaped bodies in 

 their interior. 



A weak solution of chromic acid also seems to facilitate the 

 decomposition of the medullary layer, while it renders the fibrils of 

 the fibrinous layer more consistent. If, therefore, some bundles of 

 fresh nerve fibres are put in such a solution and examined on the 

 following day, it will be found that the fibrils of the fibriUous layer 

 have only shghtly assumed a wavy appearance, and almost entirely 

 preserved their original parallel position. In the axis of the nerve 

 fibre, the naked axis cylinder is seen surrounded by a finely-granular 

 transparent hquid, and frequently found projecting for some distance 

 beyond the open end of the fibre (Fig. 13). In some cases, a number 

 of the above-described hexagonal vesicles are also observed, on which, 

 however, no further changes in form can now be discovered by the 

 application of ether. From this, it seems that they are formed 

 during the decomposition of the medullary layer, and mainly consist 

 of the fat-like constituents with an albuminous covering, which, in 

 these instances, is coagulated by the action of the chromic acid. 

 On nerve fibres of the ox, which had been laying for ten months 

 in a mixture of nine parts of water and one of alcohol, the same 

 observations were made. While the tubular membrane was pre- 

 served, the contents of the fibres, with the exception of some accu- 

 mulations of these hexagonal vesicles, had entirely disappeared. 

 Although, by the addition of ether, larger and smaller fat-like 

 masses were seen to escape from the open ends, no change of form 

 was observed in the vesicles, they were only rendered a little 

 clearer. 



From what has been said thus far, it is seen that in examining 

 fresh nerve fibres in water an endosmotic current of this liquid 

 takes place, in consequence of which they swell and frequently gain 

 considerably in diameter. Just the contrary is observed on fresh 



