CHAPTER XVI. 193 



ARNSTEIN (Anat. Anz., 1887, p. 551) puts the tissue for half an 

 hour into saturated aqueous solution of picrate of ammonia. 



S. MAYER (Zeit. wiss. Mik., vi, 1889, p. 422) preferred a mixture 

 of equal parts of glycerin and saturated picrate of ammonia solu- 

 tion, which served to fix the colour and mount the preparations in. 

 This was also in principle the method of RETZIUS (Intern. Monatsschr. 

 Anat. Phys., vii, 1890, p. 328). 



DOGIEL (Encycl. Mik. Techn., ii, p. 105) puts for two to twenty- 

 four hours into saturated aqueous picrate of ammonia, and then 

 into equal parts of glycerin and the picrate solution. (Thin mem- 

 branes, and the like, may be fixed with 1 or 2 per cent, of 2 per cent, 

 osmic acid solution added to the picrate solution and stained with 

 picro-carmine before putting into the glycerin mixture.) 



Other workers have employed saturated solution of iodine in 

 iodide of potassium (so ARNSTEIN) or picro-carmine (so FEIST, 

 Arch. Anat. Entwickel., 1890, p. 116 ; cf. Zeit. wiss. Mik., vii, 1890, 

 p. 231), the latter having the advantage of preserving the true blue 

 of the stain if it be not allowed to act too long, and the preparation 

 be mounted in pure glycerin. 



Picric acid has been used by LAVDOWSKY, but this after careful 

 study is rejected by DOGIEL. 



APATHY (op. cit., 342) brings preparations either into a concen- 

 trated aqueous solution of picrate of ammonia free from picric acid, 

 and containing 5 drops of concentrated ammonia for every 100 c.c. ; 

 or, which is generally preferable, into a 1 to 2 per cent, freshly 

 prepared solution of neutral carbonate of ammonia saturated with 

 picrate. They remain in either of these solutions, preferably in the 

 dark, for at least an hour. They are then brought into a small 

 quantity of saturated solution of picrate of ammonia in 50 per cent, 

 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 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 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. Farrants' medium [with 

 omission of the arsenious acid] will also do. In neither case should 



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