METHOD XII. 



MARCHI'S METHOD. 



A differential method for degenerating medullated nerve 

 fibers. Useful for the study of the course and distribution of 

 medullated fiber-tracts after lesions. Maybe applied to periph- 

 eral nerves as well as to the central nervous system. Also 

 differential for fatty degeneration of nerve-cells and blood 

 vessels. 



REAGENTS REQUIRED. 



A. Mullers fluid.— 



For formula see XI, A, p. 69. For the amount of tissue ordinarily 

 required, make up 500 cc. 



B. Differentiating fluid. — 



MuUer's fluid (A), 2 parts. 



I per cent, osmic acid (see IX, A, p. 55), i part. 

 Prepare just before using. 



C. Clearing fluid (carbol-xylol). — 



Xylol, 3 parts. 



Carbolic acid (melted by heat), i part. 

 Pure xylol will do, but the mixture clears more rapidly. 



Various modifications of the method have been tried since 

 its publication by Marchi in 1887,' and since his late paper in 

 1893,'' but little or no improvement has been made. 



The differential action of the osmic acid results from the fact 

 that chromic acid and its salts deprive the normal myeline sheaths 

 of the nerve fibers of their power of reducing the osmic acid 

 (tetroxide of osmium), while the chemically changed degenerat- 

 ing or abnormal sheaths retain this power. The method, therefore, 

 gives positive black images of the fibers in a state of degenera- 

 tion, while the normal fibers remain unstained, or rather are 



' Marcki, Hevisia sperim. di Freniatria e di Med. legale, li^l. 

 ^ Zeitschrift filr wissenschaftliche Mikroskopie, Bd. IX, H. 3, 1893. 



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