142 CHAPTER XII. 



made with alum, or cochineal-alum carmine ( 216), owes its 

 staining-power to the formation of carminate of alumina 

 (last ). The tincture made with pure alcohol, on the other 

 hand, contains only the above-mentioned carminate of some 

 alkali. This carminate alone stains weakly and diffusely 

 (like carminic acid alone). But if in the tissues treated with 

 it it meet with lime salts, alumina or magnesia salts, or even 

 metallic salts capable of combining with it and forming 

 insoluble coloured precipitates in the tissues, then a strong 

 and selective stain may result. And if the necessary salts 

 be added to the tincture itself, there results a solution 

 containing the necessary elements for affording a strong and 

 selective stain with all classes of objects. Hence Mayer's 

 new formula, 236. 



213. General Remarks. Carmine stains are chiefly used for 

 staining entire objects, or tissues in bulk. In most cases 

 this can be done more satisfactorily by means of carmine 

 than by means of any other known agent. For most 

 haBmatein solutions have a disastrous tendency to overstain ; 

 and the tar-colours are generally inapplicable to staining in bulk. 



Grenadier's alcoholic borax-carmine may be recommended 

 to the beginner as being the easiest of these stains to work 

 with : or para-carmine, for objects which require a highly 

 alcoholic solution. Carmalum, or one of the alum-carmines, 

 is also an easy and safe reagent. 



Overstains may in all cases be washed out with weak IIC1 

 (e. <j. O'l per cent.). Alum-solution will often suffice, or, 

 according to HENNEGUY (Journ. de I'Anat. et de la PhysioL, 

 xxvii, 1891, p. 400), permanganate of potash. All carmine 

 stains, with the exception of ace to-carmine, are permanent 

 in balsam. The alum-carmines are fairly permanent in 

 glycerin. None of the acid stains, nor any of Grenadier's 

 fluids, should be used with calcareous structures that it is 

 wished to preserve, unless they be taken in a state of extreme 

 dilution. 



A. AQUEOUS CARMINE STAINS. 

 a. Acid. 



214. Alum-carmine (GKKNACHER, Arch. mik. Anat., xvi, 1879, 

 p. 465). An aqueous solution (of 1 to 5 per cent, strength, 



