94 CAKMiNE AND COCHINEAL STAINS. 



CHAPTER X. 



CARMINE AND COCHINEAL STAINS. 



144. The Theory of Carmine Staining. I take the following 

 from the important paper of MAYBE, " Ueber das Farben mit 

 Carmin, Cochenille, und Hamatein-Thonerde," in Mitth. a. d. 

 Zool. Station zu Neapel, Bd. x, Heft 3, 1892, p. 480. The 

 rationale of staining with carmine has hitherto been obscured 

 by the erroneous notion that carmine is nothing but carminic 

 acid with at most certain impurities. This is not the case. 

 According to the analysis of LIEBEEMANN (Ber. d. Chem. Ges., 

 Jahrg. 18, 1886, pp. 1969 1975) carmine is a very peculiar 

 alumina-lime-protein compound of carminic acid, a true chemi- 

 cal compound from which at all events aluminium and 

 calcium can no more be absent than sodium from salt. 

 Analysis gives about 17 per cent, of water, 20 per cent, nitro- 

 genous matters, 56 per cent, carminic acid, at least 3 per 

 cent, alumina, and 3 per cent, lime, together with a small 

 proportion of magnesia, potash, soda, phosphoric acid, and a 

 trace of wax. Mayer has come to the conclusion that in the 

 processes of histological staining (not of industrial dyeing) 

 the active factors of the compound are, besides the carminic 

 acid, only the alumina, and, in some cases, the lime. The 

 other bases are inactive ; the nitrogenous matters, so far as 

 they have any influence at all, are an obstacle, as it is they 

 that give rise to the well-known putrefaction of the solutions. 



Having arrived at these conclusions, it seemed logical to 

 admit that carminic acid, instead of carmine, should be taken 

 as the basis of staining solutions. This had already been pro- 

 posed by DIMMOCK, whose paper (Amer. Natural., xviii, 1884, 

 pp. 324-7) I quoted at length in the first edition of this work. 

 But Dimmock's proposals were not very successful, for the 

 reason that he had omitted from his solutions the essential 

 element, the alumina. He stained, for instance, with pure 



