CHAPTER IX 

 NATURAL DYES 

 THE NATURAL DYES 



AS STATED in Chapter II the group of natural dyes is 

 l\ shrinking, as more and more of them are being produced by 

 ■^ -^ artificial means. Alizarin, for example, in the form of 

 madder, used to be extracted from the roots of Ruhia tinctor- 

 um; but the artificial manufacture of 4:his dye is now much more 

 economical. The group of natural dyes, as ordinarily recognized, 

 contains only those which are not yet produced by artificial 

 means. Indigo, however, is listed in this chapter, because in its 

 chemistry it does not fall in well with any of the groups of artificial 

 dyes. It is still obtained in part, moreover, from the indigo plant, 

 although under present-day conditions its artificial manufacture 

 is ordinarily the more economical. Similarly, orcein can now be 

 synthetically prepared, but is still included in this chapter because 

 of its relationship to other dyes that are secured from natural 

 sources only. 



The chemistry of the natural dyes is less definitely known than 

 that of the artificial dyes. This is easily understood; for it will be 

 recalled that there are two ways of obtaining information as to the 

 chemistry of unknown compounds: the first by decomposing them 

 into simpler compounds of known composition; and the second by 

 manufacturing them from known compounds. In the case of dyes 

 not yet prepared artificially the second of these two lines of pro- 

 cedure is out of the question; hence there is special difficulty in 

 learning their exact chemical structure. 



The most important natural dyes for the biologist are hema- 

 toxylin, indigo, cochineal (and its derivatives), orcein, and litmus. 



u5 Saffron 



A natural pigment of uncertain composition extracted from the 

 stigmas of Crocus sativus. It has been employed by Masson (see 

 Foot, 1933) in a connective tissue stain. A special application of 

 this procedure has been made by Block and Godin (1936) for 

 staining yellow fever lesions in the liver. A later application by 

 Van Hoecke and Sebruyns (1952) calls for this dye, after Bismarck 

 brown, aniline blue W.S. and hematein, as a differential stain for 

 glandular cells of the stomach. 



The Indigo Group 

 uio INDIGO c. I. NO. 1177 



Synonym: Indigo blue. 

 The plants from which indigo was formerly exclusively manu- 



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