532 MYELIN STAINS 



which have been damaged post-mortem, by stretching or bending, 

 and the lack of permanency of the preparations when mounted 

 in Canada balsam. To avoid these troubles it is necessary to pay 

 great attention to detail in carrying out the methods, and even 

 then the results are sometimes disappointing. Failure of penetra- 

 tion may be avoided by using plenty of osmic acid on very thin 

 blocks of tissue or on frozen sections, or by the addition of nitric 

 or acetic acid as recommended by Vassale and Orr. Mounting 

 direct from 95 per cent, alcohol in an alcoholic resinous medium, 

 such as Gurr's neutral mounting medium or " euparal," which 

 avoids strong fat solvents such as benzene, chloroform or xylol, 

 renders the stain more permanent. 



1080. Marchi's Method (Riv. Sperim. Fren., xii, 1886, p. 50). 

 Small pieces of nervous tissue are hardened for a week in Miiller's 

 solution, and then put for a few days into a mixture of 2 parts 

 of Miiller's solution and 1 part of 1 per cent, osmic acid. Sections 

 are cut, best without imbedding, and mounted in balsam. The 

 myelin sheaths of normal nerve fibres take a yellowish-brown 

 colour, those of degenerated fibres a black one. 



For a critical review of this method and its modifications, see 

 Weigert (Ergebn. AnaL, vii, 1897 (1898), pp. 1—8) ; Matus- 

 ZEWSKi (Arch, path, Anat., clxxix, 1905, p. 12) ; De Lange {Le 

 Nevraxe, x, 1908, p. 83) ; and Lewy {Fol. NeurohioL, ii, 1909, 

 p. 471). 



De Lange suggests putting pieces 3 to 4 mm. thick first for 

 a few days into a mixture of 3 parts Miiller's fluid + 1 part of 

 1 per cent, osmic acid, strengthening the osmic gradually up to 

 equal parts of 1 per cent, osmic acid and of Miiller's fluid. 



Orr {Jourti. Path, and Bad., vi, 1900, p. 387) recommends 

 original fixation for from two to four weeks in Miiller's fluid, 

 from which thin pieces are put into 2 per cent, osmic acid 8 c.c. 

 -f- 1 per cent, acetic acid 2 c.c. 



Vassale {Arch. Ital. Biol., xxvii, 1897, p. 131) takes 75 c.c. 

 of Miiller's solution, 25 c.c. of 1 per cent, osmic acid, and 20 drops 

 of nitric acid. 



Teljatnik {Neurol. Centrbl., xvi, 1897, p. 521), puts fresh 

 pieces of brain 15 mm. thick into weak Marchi's fluid and then 

 into a more concentrated solution. 



NissL {Encycl. mik. Technik., ii, p. 248), holding that alcohol 

 attacks the myelin, cuts without imbedding, and hurries sections 

 through alcohol and bergamot oil into balsam. 



Ramon y Cajal {Trah. lab. Biol. Madrid, ii, 1903, p. 93) has 

 a complicated method of treating Marchi material. 



BuscH {Neurol. Centrbl., xvii, 1898, p. 476), puts thin slices of 

 formol fixed material directly into a solution of 1 part osmic acid, 

 3 parts of sodium iodate and 300 of water. This method gives 

 the same results as Marchi's, exce})t that the background remains 



