100 CAEMINE AND COCHINEAL STAINS. 



154. Cochineal Alum-Carmine (PAKTSCH, Arch. f. mik. Anat., 

 xiv, 1877, p. 180). Powdered cochineal is boiled for some 

 time in a 5 per cent, solution of alum, the decoction filtered, 

 and a little salicylic acid added to preserve it from mould. 



Another method of preparation has been given by CZOKOR 

 (Arch.f. mik. Anat., xviii, 1880, p. 413). Mayer has care- 

 fully examined both, and finds that Partsch's is the more 

 rational, the proportion of alum in it being exactly right, 

 whilst in Czokor's it is insufficient. Partsch's fluid has also 

 the advantage of keeping better. 



The formula known as Klein's cochineal fluid (which appears to have been 

 first published in the Ann. and Mag. Nat. Hist., viii, 1881, p. 232) is iden- 

 tical with that of Czokor. 



Both these solutions are to all intents and purposes " alum- 

 carmines. J) They give a stain that is practically identical 

 with that of alum-carmine made from carmine, with perhaps 

 even more delicate differentiations (but that depends so much 

 on the quality of the carmine, the quality of the cochineal, 

 and the nature of the objects to be stained, that no absolute 

 rule can be stated). On the whole it seems to be a mere 

 matter of convenience whether the one or the other should be 

 preferred. The cochineal fluids should be used in exactly the 

 same way as the carmine fluid. 



It has been lately recommended by HERRICK (Journ. Comp. 

 Neur., Cincinnati, vol. i, 1891, p. 134) as a "vast improve- 

 ment" to make the solution with sulphate of aluminium 

 instead of alum (quoted from Mayer's paper, Mitth. Zool. Stat. 

 Neapel, 10,3, 1892, p. 496). 



155. Alum-Carmine with Osmic Acid (ZOLTAN VON ROBOZ, in 

 lilt.). To 50 or 60 grins, of water is added alum-carmine 

 until the mixture is of an almost red rose colour ; about ten 

 drops of a y^Vo" solution of osmic acid are then added. (The 

 mixture should have an appreciable smell of osmic acid.) The 

 objects to be stained remain in the mixture for from twenty- 

 four to forty-eight hours in the dark. It is hardly necessary 

 to wash them, as the stain is perfectly precise without that. 

 It is important to perform the staining in a well-closed vessel, 

 in order to prevent the evaporation of the osmium. 



I have used this stain with the most diverse objects, and can 

 most highly recommend it. The result is a sharp nuclear 



