86 METHYLEN -BLUE, AND OTHER ANILINS. 



glycerin, where they remain until thoroughly saturated. They 

 are then removed into a saturated solution of the picrate in a 

 mixture of 2 parts 50 per cent, glycerin, 1 part cold saturated 

 sugar solution, and 1 part similarly prepared gum-arabic solu- 

 tion. When thoroughly penetrated with this they are removed 

 and mounted in the following gum- syrup medium (1. c., p. 37) : 

 Picked gum-arabic . . .50 grms. 



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. 



None of the preceding methods can be said to be anything 

 like perfectly satisfactory. The stain is generally not pre- 

 served in its true blue colour, but turns to a grey, varying in 

 tone from reddish brown to bluish or greenish black. The 

 preparations seldom keep even in that state for more than a 

 very few months, and it is not satisfactory to be obliged to 

 mount preparations only in aqueous media. A strong solution 

 of platinum chloride is said to give a fixation that will resist 

 the treatment necessary for imbedding either in celloidin or 

 paraffin (see FEIST, Arch. f. Anat. und Entw., 1890, p. 116; 

 Zeit. /. wiss. Mik., vii, 2, 1890, p. 231) ; but the precipitate 

 it gives is a flocculent one, and the preparations are not very 

 satisfactory. 



The method of PARKER (Zool Anzeig., No. 403, 1892, p. 375) 

 is therefore a most welcome step forwards. The stain is fixed 

 (1) (in the form of a finely grained purplish precipitate) by 

 cold concentrated aqueous solution of corrosive sublimate. 

 The preparations are dehydrated (2) in a solution composed 

 of 1 grm. of sublimate and 5 c.c. of methylal (pure methylal 

 washes out the stain to a certain extent). The methylal 

 solution is now removed by means of a mixture (3) of two 

 parts xylol, one part pure methylal, and one part of the 

 dehydrating mixture (2). After a short time the preparations 

 are placed in (4) a considerable quantity of xylol. Here they 

 should remain till all the methylal is replaced by xylol and 

 the corrosive sublimate completely washed out. This will 



