136 CARMINE AND COCHINEAL STAINS. 



alumina or magnesia salts, or even metallic salts capable of com- 

 bining 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. 



215. 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 hgematein solutions have a disastrous 

 tendency to overstain ; and the tar-colours are generally inapplicable 

 to staining in bulk. 



Grenacher'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 HC1 (e.g. 

 0-1 per cent.). Alum-solution will often suffice, or, according to 

 HENNEGUY (Journ. de TAnat. et de la PhysioL, xxvii, 1891, p. 400), 

 permanganate of potash. All carmine stains, with the exception of 

 aceto-carmine, are permanent in balsam. The alum-carmines are 

 fairly permanent in glycerin. None of the acid stains, nor any of 

 Grenacher'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. 



216. Alum-carmine (GRENACHER, Arch. mik. Anat., xvi, 1879, 

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

 other strength that may be preferred) of common or ammonia alum 

 is boiled for ten to twenty minutes with J to 1 per cent, of powdered 

 carmine. (It is perhaps the safer plan to take the alum solution 

 highly concentrated in the first instance, and after boiling the carmine 

 in it dilute to the desired strength.) When cool, filter. 



This stain must be avoided in the case of calcareous structures 

 that it is wished to preserve. 



TIZZONI (Bull. Sc. Med. Bologna, 1884, p. 259), PISENTI (Gass. degli 

 Ospeiali, No. 24 ; Zcit. wiss. Mik., ii, 1885, p. 378), and GRIEB (Mem. 



