210 On the Construction of the 



lustre, wliich are seen to escape from the interior through the open 

 ends of the nerve fibre (Fig. 6), consist of nothing else but those 

 fibrinous coils, loops, &c., &c., just described, covered hy the semi- 

 fluid medullary layer ivhich possesses a fat-like lustre. The cause 

 of the apparent double contoui', by which they are bordered, has 

 also, like that of the entire nerve fibre, been ascribed to coagulation. 

 It will be found, however, that while that of the nerve fibre is dis- 

 tinguished by two dark, sharply-defined lines with a clear space 

 between them, that of those irregularly-shaped fat-like masses or 

 supposed myelin figures possesses a greenish lustre, and is mostly 

 represented by only one real border line. A critical examination 

 will show that the contour always corresponds to a winding of a 

 fihrillous hundle (Figs. 6, 7, 11, and 12), and that in the most 

 cases the individual fibrils may be recognized (Fig. 8). The clear 

 space between the shining greenish margins and windings is of a 

 bluish-grey hue, belonging, to the peculiar lustre of fatty masses, as 

 they appear under the microscope, and represents the covering of 

 the adhering portion of medullary layer. To remove all doubts 

 concerning the nature of these bodies, some drops of ether are made 

 to run under the covering glass, while a small piece of blotting- 

 paper is applied opposite to this point ; the ether at once dissolves 

 the fat-Hke covering and causes the individual fibrils to appear. By 

 a continued action of this reagent, however, the latter will coagulate 

 and appear granulous. 



When nerve fibres are prepared and examined in serum, and 

 only gradually exposed to the action of water, wavy bands of a 

 greenish lustre are frequently observed to remain behind in their 

 interior. These also represent fibriUous bundles covered by the 

 shining, fat-like constituents of the medullary layer ; their fibrillous 

 character is proved by the application of ether, or, even, a continued 

 action of water upon them will bring out the individual fibrils of 

 which they are composed. Judging from the last-mentioned fact, 

 the substance of the meduUary layer must be partially soluble in 

 water. 



Besides these constituents of the medullary layer which are 

 distinguished by their fatty lustre, a great number of fine pale 

 molecules or granules are observed attached to the fibrillous loops 

 escaping from the open end of the nerve fibre (Figs. 4 and 13). 

 These probably consist of some consistent albuminous body, but 

 whether in a natural or coagulated state, I do not venture to decide. 

 In the nerve fibres of the alhgator or turtle, they seem to be most 

 distinct. 



The first traces of decomposition of the nerve-medulla in the 

 interior of the nerve fibre manifest themselves by the appearance of 

 a number of vesicles (Fig. 4). They show a fine double contour, 

 and vary considerably in their diameter, measuring from ttAtt to 



