ITS MICRO-CHEMICAL RELATIONS. 105 



an uncommonly fine granular indistinct body, and it is only in rare 

 cases, although then with extreme distinctness, that the axis-cylin- 

 ders can be recognised in the individual fragments of nerves. 

 The fluid containing granules and viscid globules, and sur- 

 rounding the partially undestroyed nerves, is likewise of a violet 

 colour. 



Chromic acid, or a saturated solution of the bichromate of potash, 

 when decomposed with a little sulphuric acid, contracts the trans- 

 verse diameter of the nerve-fibres, and imparts to them an intense 

 yellow colour. After the nerve-fibres have been immersed for a 

 considerable time in this fluid, they appear somewhat narrower, but 

 sharply defined (the double contours of the animal nerve-fibres 

 are, however, no longer visible) ; the nerve-pulp becomes more 

 coarsely granular and renders the fibres opaque, so that the axis- 

 cylinder can no longer be seen within them. The contracting 

 action of this reagent on the sheath is very beautifully and dis- 

 tinctly shown ; we observe at different spots irregular, nodular, 

 but most commonly roundish drops of nerve-fat protruding from 

 it. When the action of the chromic acid is not too strong, the 

 sheath exhibits rents, from which the viscid nerve-pulp exudes, 

 and this appearance is so clearly defined that it is impossible to 

 refer it to any deception. The sheath is completely burst or 

 destroyed at different points, and the nerve-pulp diffused through 

 the fluid, so that nothing but the pale-coloured, sharply outlined 

 filiform axis-cylinder remains visible, whilst in other nerve-tubes 

 the transition of the cylinder into slightly altered fibres may be 

 distinctly traced. With the exception of the following reagent 

 there is nothing which exhibits the morphological constituents of 

 the nerve-tubes more distinctly than chromic acid. 



This acid causes the nerve-cells in some degree to contract, and 

 generally renders their outlines more distinct. The contents are 

 scarcely rendered more grumous than they previously were, whilst 

 there is no important difference to be perceived either in the 

 nucleus or the nucleolus. The cerebral and the ganglionic masses 

 are moreover hardened by the action of chromic acid. 



An aqueous solution of iodine (or what is better), iodine in a 

 solution of hydriodic acid, colours the nerves yellow, and leaves 

 the fibres tolerably coherent, so that they may be very easily pre- 

 pared for microscopical investigation, and traced into the individual 

 filaments. After the prolonged action of the above-named fluid 

 each individual nerve-tube acquires a pale yellow appearance, and 

 becomes broader, showing a tolerably distinct contour (the animal 



