194 METHYLEN BLUE. 



either ammonium picrate or metliylen blue be added to the medium.) 

 Preparations that have been/w% differentiated ( 342) 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 for 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. 



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

 preparations that will resist the operations necessary for imbedding 

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

 chloride is said to do this (see FEIST, Arch. Anat. Entw., 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 fixes 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 brings 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 propor- 

 tions, each of these solutions having added to it 1 drop of hydro- 

 chloric 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. (The objects 

 that have been treated with one of the solutions of the sodium salt 

 are not thoroughly resistant to alcohol, so that for them it is well to 

 cool the alcohol to under 15 C.) Sections may be after-stained with 

 alum carmine, or " neutral " tar colours. 



Slight modifications of this method are given by DOGIEL (Arch. 



