MYELIN STAINS 531 



differentiates with alcohol containing a very little caustic potash, and 

 counterstains with safranin. 



1077. Congo Red. Nissl {Ztschr. zviss. Mikr,, iii, 1880, p. 398) stains 

 for three days in Congo red (5 parts to 400 of water) and differentiates in 

 alcohol with 3 per cent, of nitric acid. 



1078. Other Methods. Rothig's Vital-Scharlach VIII Counter- 

 stain (Neurol. Centrbl., xxxiii, 1914, p. 219, and xxxiv, 1915, 

 p. 265). Sections stained and differentiated by Weigert-Pal's 

 method are kept for twenty-four hours at room temperature in 

 a counterstaining fluid consisting of 90 c.c, of distilled water 

 and 10 to 20 c.c. of a solution of Vital-Scharlach VIII, saturated 

 at room temperature. They are then washed in distilled water 

 for fifteen minutes and differentiated in 70 per cent, alcohol 

 for from one or two hours up to twenty-four, when the celloidin 

 will be found to be colourless. After another wash in 96 per 

 cent, alcohol, sections are mounted as usual. Nerve-cells and 

 their processes, as well as axis-cylinders red, the latter being 

 visible within the deep blue myelin sheaths. 



The method does not succeed if the sections were previously 

 treated with an osmic acid solution. Vital-Scharlach VIII 

 may also be used as a general stain, in which case the finished 

 preparations are similar to those obtainable by the usual carmine 

 stains. 



Paladino's palladium chloride methods ; see Rendic. R. Accad. 

 Scienze, Napoli, iv, 1891, p. 14; Arch. Ital. Biol., xvii, 1892, p. 145, 

 and xix, 1893, p. 26. 



For Wolter's vanadium chloride process, see next chapter. 



Zosin's magenta red method ; see Neurol. Centrbl., xxi, 1902, p. 207. 



Pkrusini's remarks and methods for the study of the white substance 

 of the spinal cord : see Joiirn. Psychol. Neurol., xix, 1912, p. 61. 



METHODS FOR DEMONSTRATING DEGENERATED NERVE- 

 FIBRES AND THE PRODUCTS OF MYELIN DEGENERATION 



1079. Among the most satisfactory methods of demonstrating 

 degeneration of myelin in either the central or peripheral nervous 

 systems, must be counted such fat stains as Scharlach R or Sudan 

 III. These can only be used for formol fixed material and either on 

 frozen sections or after imbedding in gelatin as recommended by 

 Koch (Berl. Klin. Wochenschr., li, 1914, p. 422). For anatomical 

 work, however, Marchi's method or one of its modifications is to be 

 preferred, as the degenerated fibres are stained black and stand 

 out sharply against a yellowish background. Osmic acid, as in the 

 Marchi method, undoubtedly stains some of the earlier products 

 of myelin degeneration, which are not demonstrated with Schar- 

 lach, but it has several disadvantages. Among these are the 

 difiiculty of penetrating the blocks thoroughly with the osmic 

 acid, the tendency for black granules to appear on any fibres. 



