CHAPTER XII. 



CARMINE AND COCHINEAL STAINS. 



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

 from the important paper of MAYER,, " TJeber das Farben 

 mit Carmiu, Cochenille, und Hainatem-Thonerde,' J 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 LIEBERMANN (Ber. d. 

 Chem. Ges., Jalirg. 18, 1886, pp. 19691975) carmine is a 

 very peculiar alumiiia-lime-protein compound of carminic acid, 

 a true chemical compound from which at all events aluminium 

 and calcium can no more be absent than sodium from salt. 

 Analysis gave him about 17 per cent, of water, 20 per cent, 

 nitrogenous matters, 56 per cent, carminic acid, at least '6 

 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, always 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 solu- 

 tions. 



Having arrived at these conclusions, it seemed logical to 

 admit that carminic acid, instead of carmine, should l>e taken 

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

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

 pp. 3247) I quoted at length in the first edition of this work. 

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



