102 NERVOUS TISSUE. 



project from the extremities of the torn nerve-fibres ; they can 

 often be traced for some distance along the uninjured nerve- 

 tube, and are unquestionably axis-cylinders. Kolliker has noticed 

 the difficulty and slowness with which these filaments dissolve 

 even on being boiled with concentrated acetic acid. When con- 

 centrated acetic acid is added to a nerve-fibre whilst under the 

 microscope, the nerve is seen to retract instantaneously, whilst the 

 granular nerve-pulp and very pale fibres, which are evidently 

 the axis-cylinder, project from the cut ends (Kolliker). The fine 

 nerve-fibres of the sympathetic system also swell in acetic acid, 

 their contents become grumous, whilst at different spots an axis- 

 cylinder becomes visible under favourable circumstances. Besides 

 these fibres we may frequently discover the pale nucleated fibres 

 of Remak; we must, however, be careful not to confound them 

 with the fibres of connective tissue, which also exhibit many 

 narrow nuclei in the cerebro-spinal nerves on the addition of 

 acetic acid. (F. P. 15, F. 6.) 



It will be found that the behaviour of the nerve-cells towards 

 acetic acid precisely accords with the account given by Kolliker. 

 The individual parts of the cell generally become somewhat more 

 visible in dilute acid ; the cell-membrane exhibits a more distinct 

 contour, the contents of the cells become more granular and often 

 more turbid, but notwithstanding this the nucleus notunfrequently 

 appears distinctly visible. Concentrated acetic acid, after pro- 

 longed action or on the application of heat, causes the cell- 

 membranes to swell till at length they become wholly invisible. 

 The granular contents are dissolved, with the exception of the 

 darker granules, which occur in some of the cells ; and even the 

 nuclei, which at first come more distinctly into view, finally 

 disappear. 



Very dilute hydrochloric acid (1 part in 12,560 parts of water) 

 causes the nerve-fibre to swell, and renders the contents far more 

 transparent. The separate fibres exhibit beautiful, sharply defined 

 double contours ; between which there remains in the middle a 

 perfectly transparent, tolerably broad space, which appears almost 

 empty. Neither nerve-sheath nor axis-cylinder can anywhere be 

 distinctly recognised. The delicate fibres of the sympathetic are 

 not visibly altered in this very dilute solution of the acid, but the 

 nuclei of Remakes fibres, as well as those of the connective tissue, 

 are brought more prominently to view. 



There is very little alteration perceptible in the nerve-cells, 

 even after a very prolonged action of this solution of the acid ; 



