THE NERVOUS SYSTEM. 839 



the gray and white matter of the nerve tissue. The exact degree of decolorizatiou 

 which gives the best pictures will be learned by practice of tfie method. In many cases 

 the use of alcohol alone without aniline oil is preferable to the mixture, and in any cast 

 the sections should always be washed in strong, pure alcohol before passing on to the 

 xylol. The sections are now freed from the bulk of the alcohol upon the slide, cleared 

 in xylol, and mounted in dammar varnish, in which the color is apt to be preserved 

 better than in balsam. By this procedure the chromophilic bodies in the cytoplasm of 

 ganglion cells are sharply differentiated, and thus abnormal conditions may be detected 

 in them (see Plate XIII.). 



A contrast stain with erythrosin (Held ') is useful in demonstrating cell structures 

 which are not visible with the simple Nissl staining. This may be secured as follows : 



The sections are first warmed from one to two minutes in the following solution : 

 erythrosin, gm. 1; acetone, gtt. ij.; aqua dest., 150 c.c. They are then washed thor- 

 oughly in water and transferred to a solution consisting of equal parts of Nissl 's methy- 

 lene blue solution and a five-per-cent aqueous solution of acetone. In this they are 

 warmed until the odor of acetone ceases to be given off. The sections are decolorized 

 in a one-tenth-per-cent solution of alum until they appear red in color, and are then de- 

 hydrated in alcohol and cleared and mounted in the usual way. 



1 Held, Arch. f. Anat. und Phys., anat. Abt., 1895, p. 396; 1897, p. 204. 



