METHYLEN BLUE. 209 



thickness are treated for ten to fifteen minutes with a con- 

 centrated aqueous solution of picrate of ammonia and then 

 brought into a solution of 1 grin, 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 

 hydrochloric acid, and if desired 1 grin, 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 15C.) Sections may be after- 

 stained with alum carmine, or " neutral " tar colours. 



Slight modifications of this method are given by DOGIEL 

 (Arch. mik. Anat., xlix, 1897, p. 772; liii, 1898, p. 237; 

 Zeit. wiys. ZooL, Ixvi, 1899, p. 361 ; and EncycL mik. Technik, 

 1903, p. 825, and 1910, p. 108). He omits the peroxide, 

 the hydrochloric acid, and the cooling. Bethe (Zeit. wiss. 

 Mik., xvii, 1900, p. 21) does not approve of these modifications. 



Further modifications of the molybdenum method have 

 been published by LEONTOWITSCH (Intern. Monatsschr. Anat., 

 xviii, 1901, p. 142). 



MICHAILOW (Zeit. wiss. Mik., xxvii, 1910, p. 19) adds to 

 8 per cent, solution of molybdate 0'5 per cent, of formalin, 

 leaves the objects in a large quantity of it (filtered) for 24 

 hours at 37 C., washes with warm water, and passes through 

 alcohol and xylol into xylol-damar (not balsam). 



See also SCHMIDT (Arch. Ges. Phys., ciii, 1906, p. 522). 



HARKIS (Philadelphia Medical Journ., May 14th, 1898), 

 after staining, rinses with water, and brings into a saturated 

 solution of either ferrocyanide or ferricyanide of potassium 

 which has been cooled to within a few degrees of zero 

 (a trace of osmic acid may be added to prevent macera- 

 tion). They remain therein for three to twenty-four 

 hours, and are then washed in distilled water for an hour, 

 and are dehydrated in absolute alcohol kept at a low 

 temperature, cleared in xylol or cedar oil, and imbedded in 

 paraffin. 



14 



