104 NERVOUS TISSUE. 



interspace, or bright central stripe : the nerve-tubes are generally 

 found to have become thinner rather than thicker, and the nerve- 

 sheath can scarcely be recognised with certainty. It is seldom, 

 however, that a microscopical preparation of this kind is thoroughly 

 examined without our detecting some nerve-fibres with the axis- 

 cylinder most distinctly projecting from one extremity like the 

 wick from a taper. Frequently, indeed, six or more of these taper- 

 like nerve-tubes may be seen, the projecting axis- cylinders of which 

 exhibit a distinct yellow colour ; these have frequently an undulat- 

 ing outline when they project to any great distance, and in some 

 rarer cases have an intestine-like coiled appearance. If fibres, 

 which have been treated with nitric aid, are boiled with absolute 

 alcohol, they become very hyaline, and their outlines grow less 

 distinct, although the yellow transparent nerve-sheath may still be 

 detected at different spots, whilst the interior exhibits a faint 

 granulation, the colour of which cannot, however, be determined 

 with certainty. The axis-cylinders are often thus seen more 

 distinctly than by the mere application of nitric acid. (F.P. 15,F. 6.) 



If we boil teased (or unravelled) nerves with alcohol and ether, 

 and after the removal of these fluids allow them to remain for some 

 time in concentrated nitric acid, the nerve-sheath, as Kolliker has 

 already observed, is brought into view, exhibiting faint granules 

 and very beautiful, often detached axis-cylinders. Under favour- 

 able conditions there is scarcely any means by which the sheath 

 and axis-cylinder can be more beautifully exhibited. 



The first effect of concentrated nitric acid upon the nerve-cells 

 is to render the cell-walls more distinct, and the contents more gran- 

 ular; the cell-membrane, however, soon disappears, and we can per- 

 ceive only the nucleus in addition to a confluent granular pulpy mass. 

 When the grey substance of the brain has been immersed for any 

 length of time in concentrated nitric acid, nothing can be recog- 

 nised in addition to the elements of the fibres, excepting nuclei 

 and nucleoli, which are the sole remnants of the nerve-cells. 



Concentrated sulphuric acid (the third hydrate) forms a fine 

 purplish red or violet fluid, after remaining for some time in con- 

 tact with the nerve-fibres. The colour resembles that which appears 

 in Pettenkofer's bile-test. The addition of sugar is not necessary 

 for the production of this colour. The separate nerve-fibres ex- 

 hibit a very beautiful violet tint when seen under the microscope; 

 the nerve- sheath, which is found to swell in a gelatinous manner 

 when sulphuric acid is added to a fresh preparation, is rendered 

 entirely invisible in this case. The nerve-pulp is converted into 



