14 CAROTINOIDS AND RELATED PIGMENTS 



and red tinted animal pigments included under the older term lipo- 

 chrome, are characterized by the ease with which they oxidize when in 

 solution or in the solid state. The earlier workers did not recognize, 

 however, that some of the most characteristic properties of these pig- 

 ments are subject to modification even in the earliest stages of oxida- 

 tion. This is particularly true of the color reactions with various 

 reagents, and the spectroscopic properties, which have been used so 

 widely, and many times exclusively, as the basis for the classification 

 of the animal chromolipoids. 



Confusion in terminology, however, has not been confined to the 

 animal pigments. The chief difficulty regarding the plant carotinoids 

 has been the proposal of names already in use for pigments of obvi- 

 ously different composition and properties. For example, the name 

 xanthophyll, as used by various workers in the field of plant pigments, 

 has been the cause of so much confusion in the nomenclature as to 

 be very disconcerting to many students of this subject. 



It is not surprising, therefore, that certain investigators have 

 attempted to bring some semblance of order to the confusion by pro- 

 posing one name to cover all the names previously proposed for pig- 

 ments of like or similar properties. A brief history of these attempts 

 with their resulting influence on the nomenclature of plant and animal 

 chromatology may prove of interest at this point. 



Luteins 



The first attempt to bring various yellow pigments together under 

 one name is found in Thudichum's (1869) classic paper, in which the 

 yellow pigments found in many tissues of both vegetable and animal 

 origin are grouped under the name "luteine," or luteins. The name 

 was obviously suggested by the fact that the characteristic yellow pig- 

 ment of the corpus luteum on the ovaries of mammals, especially that 

 of the cow, is one of the representatives of the "luteine" pigments. It 

 is doubtful whether Thudichum was familiar with the work of Pic- 

 colo and Lieben (1866), who had crystallized the corpus luteum pig- 

 ment a few years previously and named it luteohamatoidin or hamo- 

 lutein. However, Thudichum mentioned the work of Holm (1867), 

 who isolated the corpus luteum pigment and called it hamatoidin. 



Thudichum's luteins included, besides the corpus luteum pigment, 

 the yellow pigment of blood serum, adipose tissue and butter, and the 

 yellow pigment of egg yolk. The vegetable pigments in the lutein 



