MYELIN STAINS 533 



almost colourless. Penetration often appears to be more rapid, 

 but irregular black granules are sometimes found throughout the 

 tissue. This ap{)cars to be due to some impurity in the formalin 

 or to too long fixation. It can be avoided by thorough washing 

 of the material before it is placed in Busch's fluid or by refixation 

 for a few days in Miiller's fluid, thereafter washing out before 

 treating with osmie acid. 



Swank and Davenport {Stain. Tech., x, 1935, p. 87), after 

 fixing in 10 per cent, formalin for forty-eight hours, cut the tissues 

 to be stained into blocks 3 mm. thick and place them in 



1 per cent, potassium chlorate . . .60 c.c. 



1 per cent, osmie acid . . . . 20 ,, 



glacial acetic acid . . . . . 1 ,, 



37 per cent, formaldehyde gas solution 



(Merck's reagent) . . . . 12 ,, 



using about 15 volumes of reagent to 1 volume of tissue and 

 staining for seven to ten days. The blocks are then washed in 

 running water for twelve to twenty-four hours, dehydrated and 

 imbedded in celloidin. After cutting, sections may be counter- 

 stained in 1 per cent, aqueous cresyl violet for three to four minutes. 

 They are washed in 70 per cent, alcohol and differentiated in acid 

 alcohol or in equal parts of 95 per cent, alcohol and butyl alcohol, 

 washed thoroughly in several changes of 95 per cent, alcohol, then 

 passed through butyl alcohol and mounted in Canada balsam. 



Venderovic {Anat. Anz., xxxix, 1911, p. 414) washes out the 

 formalin thoroughly and lays slabs 2 to 5 mm. thick on several 

 layers of filter paper in glass bottles which are then filled with 

 Busch's fluid. The sections are occasionally turned over so that 

 penetration may take place from both sides. Large pieces are 

 kept in this a month or more, changing Busch's fluid occasionally. 

 Steensland (Anat. Rec, viii, 1914, p. 123) recommends clearing 

 sections of Marchi material with oleum origani cretici and mounting 

 in chloroform-balsam. These methods which do not involve the 

 use of Miiller's solution, have the advantage that the tissue is less 

 brittle and can be cut by the frozen section method. 



Hurst has suggested a Marchi method for frozen sections which 

 has been modified by R. C. J. Stewart {Journ. Path, and Bact.). 

 He cuts frozen sections at 30/i from formalin fixed tissues. The 

 sections are washed for one and a half hours in many changes of 

 distilled water and are then placed in 2-5 per cent, potassium 

 bichromate for twenty-four hours at 21° C. After washing in 

 distilled water until the yellow colour has almost disappeared the 

 sections are immersed in 1 per cent, osmie acid in the dark for 

 sixteen to thirty-six hours at 21° C. (overnight usually suffices). 

 They are then washed for five minutes in two changes of tap-water 

 and are differentiated, if necessary, in 0-05 per cent, potassium 

 permanganate, followed by Pal's solution, subsequently being 



