GENERAL DISTRIBUTION OF CAROTINOIDS 19 



"Carotin group." The discovery that carotin itself is a hydrocarbon 

 li-d to the adoption of the name "carotene," as proposed by Arnaud 

 1 1886). The London Chemical Society favors the spelling "carrotene" 

 for the hydrocarbon. 



Xopf (1893a, 1895) proposed to distinguish between two groups of 

 carotins, namely, eucarotins (true carotins) which were hydrocarbon 

 in nature and carotiriins, which contained oxygen as well, and formed 

 compounds with the alkali and alkaline earth metals. It should be 

 stated, however, that Zopf used the term carotin synonymously with 

 lipochrome in most of his extensive studies of the pigments of the 

 lower forms of plants and animals. His eucarotins, which were some- 

 times called yellow carotins, unquestionably contained representatives 

 of our present group of xanthophylls whose chemical relation to caro- 

 tin was not discovered until several years later. The carotinins of 

 Zopf were red in color. The belief that they contained oxygen was 

 based on the fact that they appeared to form alkali and alkali earth 

 compounds. Obviously the carotinins are not related to the oxygen- 

 containing xanthophylls, as known at the present time. None of the 

 true carotinoids so far isolated in pure, crystalline state show acid 

 properties like the so-called carotinins. The nature of the compounds 

 which the latter are stated to form with sodium, calcium and barium 

 remains to be determined, as well as their true relation to the caro- 

 tinoids. The carotinins appear to be constituents of both plants and 

 animals, as will appear from a fuller account of them given in Chap- 

 ters III and V. 



Tswett (1911a), to whose ingenuity we owe much of our knowledge 

 regarding the physico-chemical properties of the chromolipoids, has 

 proposed the term "carotinoide" for the various chromolipoids which 

 are chemically and generically related to carotin. He would desig- 

 nate as carotins all those chromolipoids whose constitution and prop- 

 erties show themselves to be hydrocarbons, and as xanthophylls all 

 those whose constitution and properties show themselves to be oxy- 

 hydrocarbons and which are chemically, as well as generically, related 

 to carotin. 



Tswett's terminology has been widely adopted. The author has 

 also used it consistently in his own writings. The term carotinoid has 

 the objection, however, that the -oid ending is derived from the Greek 

 ei5i>$, shape, so that strictly speaking the carotinoids are pigments 

 which resemble carotin in form or structure only. As yet nothing 

 definite is known regarding the structure of the carotinoids. The 



