196 METHYLEN BLUE 



gum-arabic solution. When thoroughly penetrated with this they 

 are removed and mounted in the following gum-syrup medium 

 {loc. cit., p. 37) : 



Picked gum-arabic . . . .50 grm. 



Cane-sugar (not candied) . . . 50 ,, 



Distilled water . . . . . 50 ,, 



Dissolve over a water-bath and add 0-05 grm. thymol. (This 

 mounting medium sets quickly and as hard as balsam, so that 

 no cementing of the mounts is necessary. Farrant's medium 

 [with omission of the arsenious acid] will also do. In neither 

 case should either ammonium picrate or methylen blue be added 

 to the medium.) Preparations that have been f idly differentiated 

 (§ 381) do not keep more than a few weeks ; whilst those in which 

 the differentiation has not been carried to the point of thorough 

 tinctorial isolation of the neuro-fibrils have kept ^or five or six 

 years (Apathy, Mitth. Zool. Stat. Neapel, xii, 1897, p. 712). 



Pleschko {Anat. Anz., xiii, 1897, p. 16) fixes with picrate, and 

 then puts into 10 per cent, formol for a few days. 



The methods described next § are also available for material 

 not destined to be sectioned. 



383. Methods for Sections. The preceding methods do not give 

 preparations that will resist the operations necessary for imbed- 

 ding in paraffin or mounting in balsam. A strong solution of 

 platinum chloride is said to do this (see Feist, Arch. Anat. Entrv., 

 1890, p. 116), but the preparations are not very satisfactory. 



For the earlier method of Parker {Zool. Anzeig., 1892, p. 

 375) with methylal, see early editions. Later {Mitth. Zool. Stat. 

 Neapel, xii, 1895, p. 4) he fixed the stain by dehydrating the 

 objects in successive alcohols of 30, 50, 70, 95 and 100 per cent, 

 strength, each containing 8 per cent, of corrosive sublimate, 

 then brought them into a mixture of the last with an equal volume 

 of xylol, and lastly into pure xylol. 



For the earlier method of Bethe {Arch. mik. Anat., xliv, 1894, 

 p. 585), see last edition. 



Bethe's later method {Anat. Anz., xii, 1896, p. 438) is as 

 follows : After staining, pieces of tissue of 2 to 3 mm. thickness 

 are treated for ten to fifteen minutes with a concentrated aqueous 

 solution of picrate of ammonia and then brought into a solution 

 of 1 grm. of molybdate of ammonium, either in 20 of water, or in 

 10 of water and 10 of 0-5 per cent, osmic acid or 2 per cent, chromic 

 acid ; or into a solution of phosphomolybdate of sodium in the 

 same proportions, each of these solutions having added to it 1 drop 

 of hydrochloric acid, and if desired 1 grm. of peroxide of hydrogen. 

 They remain in one of these solutions for three-quarters to one 

 hour (or from four hours to twelve in the osmic acid one), and are 

 then passed through water, alcohol, xylol, balsam, or paraffin. 



