214 Biological Stains 



this techiiic the iron alum is applied first to the tissues as a mor- 

 dant, and then followed by the stain. In Hansen's ferri-cochineal, 

 on the other hand, the iron alum is mixed with the dye, and the 

 mixture used for staining sections of tissue (see Lee, 1937, p. 145). 

 Reynolds (1936) has proposed a mixture of alum cochineal with 

 hematoxylin in staining trematodes and nematodes, in toto. 



Carmine. Carmine is of considerable historic interest. It was 

 used as early as 1770 by Hill and in 1838 by Ehrenberg, although as 

 stated elsewhere not exactly for histological purposes. It was 

 also employed in 1849 by Goppert and Cohn, by Corti in 1851, 

 and by Hartig in 1854-8, these being the first uses of dyes in 

 histology. It is still a valuable stain today, in spite of the enor- 

 mous variety of synthetic dyes now available. It is much used for 

 staining in bulk, particularly in embryological work. A well- 

 known formula is Schneider's aceto-carmine (see Lee, 1937, p, 

 142), which is a valuable chromatin stain for fresh material in 

 smear preparations. Belling's (1921) iron aceto-carmine is 

 valuable for staining chromosomes in smear preparations from 

 anthers. Alum carmine was used by Grenacher (1879) for similar 

 purposes. Carmine is only slightly soluble in water at a neutral 

 reaction; so solutions must be either acid (like the three above) or 

 alkaline. Three alkaline formulae are of considerable use: am- 

 monia carmine, which has been used both for injection and 

 for staining sections; soda carmine, used primarily for injection; 

 and Mayer's (1892, 1896) magnesia carmine, useful either for sec- 

 tions or for staining in bulk. Orth (1883) proposed a lithium 

 carmine (i.e., dissolved in a solution of Li2C03) as a nuclear stain 

 for tissues; and the formula for this stain, as given by Krause 

 (1926, I, p. 265), is still frequently employed. Alcoholic solutions 

 are also used : Grenacher's borax carmine (or as modified by Mayer, 

 1892, 1896) being a splendid nuclear stain for sections; and the 

 hydrochloric carmine of Mayer serving both for sections and for 

 staining in bulk. A special formula containing aluminium chloride 

 (known as muci-carmine) has been proposed by Mayer (1892, 

 1896) and is used for staining mucin. In double staining it is 

 sometimes used with indigo carmine; but most often with picric 

 acid or spirit blue. Picro-carmine is a very well-known combina- 

 tion used for double staining effects in sections, particularly for 

 nervous tissue; it stains nuclei red and cytoplasm yellow. 



One of the important uses of carmine is in Best's (1906) carmine 

 stain for glycogen. The method is simple and the result beautiful, 

 the red glycogen standing out in sharp contrast to the blue of the 

 nuclei after staining in alum hematoxylin. The stain is perma- 

 nent; the method is of much importance both to the pathologist 

 and to the histologist. 



Carminic acid. The dye principle of carmine and cochineal is 

 carminic acid. This product is obtained by extracting the insect 



