236 CHAPTER XVII. 



Phys., Bd. vii, H. 8, 1890, p. 328). DOGIEL, after careful 

 study, quite refuses to admit that this is in any way an im- 

 provement. 



Other workers have employed saturated solution of iodine 

 in iodide of potassium (so ARNSTETN) or picro-carmine (so 

 FEIST, Arch. f. Anat. u. Entwickel., 1890, p. 116; cf. Zeit. f. 

 wiss. Mik., vii, 2, 1890, p. 231), the latter having the advan- 

 tage 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 too, after 

 careful study, is rejected by DOG i EL. 



APATHY (Zeit.f. wiss. Mik., ix, 1, 1892, p. 30) has found, as 

 stated above, that free ammonia is a capital factor in the 

 differentiation of the stain. He brings preparations (after 

 washing in salt solution if the staining have been performed 

 with a strong methylen blue solution, or without washing if 

 it have been done with a very dilute solution) either into a 

 concentrated aqueous solution of picrate of ammonia free 

 from picric acid, and containing five drops of concentrated 

 ammonia for every 100 c.c. ; or, which is generally prefer- 

 able, 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 lea$t 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 pnrt 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. Fax-rants' 



medium (with omission of the arsenious acid) will also do. 



