NEUROLOGICAL METHODS. 407 



b. Myelin-and-axis-cylinder Stains. 



725. PALAUINO'S Iodide of Palladium Method (Rendic R. 

 Accad. Scienze Fis. e Mat., Napoli, iv, 1890, p. 14, and 1891 

 [1892], p. 227 ; Zeit.f. wi*s. Mil:., vii, 2, 1890, p. 237, andix. 

 2, 1892, p. 238; Journ. Roy. Mic. Soc., 1890, p. 817, and 

 1892, p. 439). Pieces of material hardened in bichromate, 

 chromic acid, or corrosive sublimate, and not more than 5 to 

 ;8 mm. in thickness, are put for two days into a large quan- 

 tity (at least 150 to 200 c.c. for each piece) of O'l per cent, 

 solution of chloride of palladium (see 78). They are next 

 put for twenty-four hours into a solution of iodide of potas 

 sium of 4 : 100 strength, of which a relatively small volume 

 should be taken ; otherwise the iodide of palladium, which 

 is rapidly formed in the tissues, may be again extracted by 

 the liquid (small pieces of tissue should not remain in it for 

 more than one or two hours) . Dehydrate ; imbed, if neces- 

 sary, in paraffin by the chloroform method ; mount in 

 balsam. 



Later (Boll. Accad. Med. Ron. a, xix, 1893. p. 256; Arch. 

 ItaL Biol., xx, 1894, p. 40) he first dehydrates the pieces, 

 then puts them in an incubator for an hour into absolute 

 alcohol and benzol, an hour in pure benzol, and finally 

 twenty-four hours in absolute alcohol, which removes the 

 myelin. They are then put for a week into chloride of 

 palladium of 1 to 2 per cent., one to two days into 4 per 

 cent, iodide of potassium, and are lastly passed through 

 alcohol into celloidin. 



726. SAHLI (Zeit. f. wiss. Mik., 1885, p. 1) stains sections of tissue 

 hardened in bichromate to the degree required for Weigert's hsematoxy'lin 

 process for several hours in concentrated aqueous solution of metliylen 

 blue, rinses with water, and stains for five minutes in saturated aqueous 

 solution of Saurefuchsin. If now the sections be rinsed with alcohol and 

 brought into a liberal quantity of water, the stain becomes differentiated, 

 axis-cylinders being shown coloured red and the myelin sheaths blue. 



The same author (loc. cit., p. 50) also gives the following: Sections of 

 material hardened as before are stained for a few minutes or hours in the 

 following liquid : 



Water 40 parts. 



Saturated aqueous solution of methylen blue . 24 

 5 per cent, solution of borax . . . . 16 ,, 

 (Mix, let stand a day, and filter.) 



