ITS MICRO-CHEMICAL RELATIONS. 109 



nucleus nor nucleolus is visible ; on the addition of water they 

 are observed to swell up, and the contours gradually to disappear 

 in the fluid ; the nuclei do not appear, and at length nothing 

 remains visible but a little granular matter. 



When preparations of nerves which have been immersed in 

 concentrated nitric acid for any length of time are brought in 

 contact with a dilute solution of potash, the granular contents 

 exude in the form of pale drops or globules from the yellow- 

 coloured portions of fibre, leaving only the empty sheaths, which 

 appear to be of an extremely pale yellow colour. This method, 

 which was first suggested by Kolliker, is, perhaps, the best adapted 

 for bringing to view the sheaths of the individual nerve-fibres. 



When nerve-fibres, which have been immersed for a consider- 

 able time in concentrated acetic acid, are treated with boiling ether 

 or alcohol, their appearance is found to differ according as these 

 agents have acted more on small bundles or on individual portions 

 of fibres. The longer portions, or the nerve-fibres that have 

 been separated by the method described in the preceding 

 paragraph, appear to be somewhat contracted when compared 

 with the thick coarsely granular fibres which have been treated 

 with acetic acid only ; the pale contours, corresponding to the 

 sheath-membrane, become distinctly visible at certain points ; 

 invested in this membrane we see short portions of a granular 

 substance, which are separated from one another by light inter- 

 mediate spaces ; there is usually no axis-cylinder to be recognised 

 in these fibres. If the acetic acid has not exerted its action for 

 too long a time, and especially if it has not been warmed, the axis- 

 cylinder may be very distinctly seen in the torn fragments of a 

 nerve-fibre after it has been treated with alcohol or ether, and its 

 projecting end may be traced for a considerable distance within 

 the tube. Very short portions of nerve-tubes seem, however, 

 to be perfectly empty, appearing like tolerably regular, very faintly 

 granular, extremely transparent cylinders, bearing some resem- 

 blance to the urinary cylinders in Bright's disease, which are 

 composed of the membrana propria of the tubes of Bellini, only 

 they are far narrower and at least equally hyaline. 



If we now proceed to consider the conclusions which may be 

 deduced from the above-described micro-chemical reactions, and 

 from others on a larger scale, we find that the following is the 

 chemical constitution of the separate morphological constituents of 

 the nerve-fibres and cells. 



The sheath of the nerve-fibres consists, according to tne above 



