146 CARMINE AND COCHINEAL 



266. As to Picro-Carmine. The term " picro-carmiue " is 

 commonly used to denote a variety of solutions in which 

 carmine, ammonia, and picric acid exist uncomhined in hap- 

 hazard proportions. These solutions do 7iot contain a double 

 salt of picric and carminic acid and ammonia, or picro-carminate 

 of ammonia. They are always alkaline, and frequently injurious 

 to tissues. The raison d'etre of picro-carmine does not lie in its 

 capacity of affording a double stain, but in that the picric acid in 

 it is supposed to neutralise the ammonia, which it only does 

 imi^erfectly. See Mayer in Zeit. wiss, Mik., xiv, 1897, p. 18. 



267. Ranvier's Picro-Carmine, Original Formula (Traite, p. 100). 

 To a saturated solution of picric acid add carmine (dissolved in 

 ammonia) to saturation. Evaporate down to one-fifth the original 

 volvmie in a drying oven, and separate by filtration the precipitate that 

 forms in the liquid when cool. Evaporate the mother liquid to dryness, 

 and you will obtain the picro-carmine in the form of a crystalline 

 powder of the colour of red ochre. It ought to dissolve completely in 

 distilled water ; a 1 per cent, solution is best for use. 



For slow staining, dilute solutions may advantageously have 1 or 2 

 per cent, of chloral hydrate added to them. 



Overstains may be washed out with hydrochloric acid, say 0-5 per 

 cent, in water, alcohol, or glycerin. 



Preparations should be mounted in balsam, or if in glycerin, this 

 should be acidulated with 1 per cent, of acetic acid, or better, formic 

 acid. 



Ranvier's Later Formula does not give a more constant product 

 (see previous editions). 



268. Van WiJHE dissolves 0-5 per cent, of the dry ammonia-carmine, 

 § 262, in a 1 per cent, solution of neutral picrate of ammonia, boils until 

 the vapour ceases to blue reddened litmus paper, and adds 1 per cent, 

 of chloral hydrate. Gives an almost neutral preparation. 



269. Mayer's Picro-Magnesia Carmine {Zeit. wiss. Mik., xiv, 1897, 

 p. 25) is relatively constant and innocuous to tissues. It consists of 

 1 vol. of the stock solution of magnesia-carmine (§ 265), and 10 vols, of 

 a 0-6 per cent, solution of picrate of magnesia, or of equal parts of the 

 iveak solution and the picrate solution. The picrate may be obtained 

 from Grubler & Hollborn, or the solution may be made by heating 

 0-25 grm. of carbonate of magnesia in 200 c.c. of 0-5 per cent, solution 

 of picric acid, allowing to settle, and filtering. 



De Groot's picro-magnesia carmine {ibid., xxix, 1912, p. 184) con- 

 tains ammonia, which is bad, and seems to us superfluous. 



270. Other Formulae for Picro-Carmine and Other Aqueous Carmines 

 (Acid and Alkaline). Lee has tried most of them, and found no real 

 advantage in any of them {see previous editions). 



B. ALCOHOLIC CARMINE STAINS 



271. Alcoholic Borax-Carmine (Grenacher, Arch. mik. Anat., 

 xvi, 1879, pp. 466 et seq.). Make a concentrated solution of carmine 

 in borax solution (2 to 3 per cent, carmine to 4 per cent, borax) 

 by boiling for half an hour or more (or allowing it to stand, with 

 occasional stirring, for two or three days) ; dilute it with about an 



