Darh or Double-bordered Nerve Fibre. 209 



disturbances satisfactorily, it must be supposed that various con- 

 ditions and circumstances may interfere with the endosmotic pro- 

 cess, so that it cannot go on at the same rate at all points of the 

 nerve fibre. At those places, therefore, where the current is 

 strongest, the penetrating water will momentarily be collected, 

 dilate the tubular membrane, and cause — especially in the vicinity 

 of a place where the endosmosis is feeble — those sack-like bulgings 

 (Fig, 3). The same process causes also the formation of those 

 loops and coils, composed of the exceedingly delicate fibrils of the 

 fibrinous layer, which are observed as well in the interior of the 

 nerve fibre as when escaping from its open ends (Fig. 4). Some- 

 times the tubular membrane is slightly torn, offering an opportunity 

 to observe distinctly the issue of the fibrillous loops in the form of 

 a hernia from the opening (Fig. 4). To explain the formation of 

 these loops and coils more perfectly, it must be taken into con- 

 sideration that the dissolution of the intermediate substance which 

 binds the fibrils to each other, does not everywhere take place in 

 the same degree, and that accordingly, the entire fibrillous layer is 

 not separated into single fibrils at once ; on the contrary, many of 

 the latter are still observed to adhere together in the form of fine 

 bundles. In an equally irregular manner, the separation of the 

 fibrils from the inner surface of the tubular membrane may take 

 place, in which case those poi-tions already loosened would be taken 

 along in the form of loops by the endosmotic current. Accord- 

 ingly, long loops are often seen in the interior of the nerve fibre, 

 floating towards its open ends with the current (Fig. 6). The 

 substance of the fibrils is so very delicate and soft, that they in 

 consequence will undergo new changes in form (caused by the 

 current), and in this manner the most irregular coils, loops, and 

 windings are frequently formed at every obstacle which they meet 

 in their course, — yes, in places where they cross each other, they 

 will run into each other (Figs. 10 and 11), and become even 

 apparently fused into an irregular clod. 



While a portion of the fibrillous layer is carried in the form of 

 loops and coils to the open end of the fibre by the current of the 

 water penetrating through the tubular membrane, the rest remains 

 in its original place, where it is now seen as fine, more or less wave- 

 like bundles of fibrils (Figs. 5, 6, 10, and 11). The disturbances 

 which this layer suffers through the endosmosis of the water, are 

 observed in a greater or lesser degree in different animals ; they 

 probably stand in some relationship with the delicacy of its compo- 

 sition. In man and other higher vertebrata in general, the fibrils 

 appear to be more delicate than in the amphibia. In the alligator 

 and turtle especially, they seem nearly to maintain their original 

 position (Fig. 13). 



Those apparently double-bordered masses of a fat-like, greenish 



R 2 



