GENERAL DISTRIBUTION OF CAROTINOIDS 15 



group included the pigment of yellow maize, and annatto seeds, the 

 pi.umrnt of the carrot root and of yellow leaves, such as those of the 

 Coh us, and the pigments which characterize the stamens and petals of 

 many flowers. 



The basis for the classification of these pigments into one group 

 was: (1) their common solubility in alcohol, ether and chloroform, 

 and in albuminous liquids like blood serum; (2) the fact that their 

 solutions showed three absorption bands in the blue, indigo and violet 

 region of the spectrum; (3) the fact that they could be crystallized 

 in the form of rhombic plates; (4) certain common chemical reactions, 

 such as their precipitation by mercuric acetate and mercuric nitrate, 

 and their blue color reaction with nitric acid, when the pigments were 

 in the solid state or in solution in acetic acid; (6) and their affinity 

 for albumin, as in blood serum and the fluid of ovarian cysts, from 

 which the pigments are extracted with difficulty. 



Thudichum's classification never received wide adoption. In fact, 

 the luteins, as defined by Thudichum, comprise a number of different 

 pigments. Moreover, our present knowledge regarding practically all 

 the pigments which were included in this classification shows that cer- 

 tain of the characteristic lutein properties 1 are specific only for cer- 

 tain individuals of the group. The final abandonment of this classifi- 

 cation appears in the recent application of the name lutein by Will- 

 st litter and Escher (1912) to the specific crystalline pigment isolated 

 by them from the yolks of hen's eggs. This use of the name appears 

 to the author to be illogical both from the standpoint of function and 

 anatomy as well as on other biological grounds. The name lutein 

 obviously suggests the body from which the name was derived, namely, 

 the corpus luteum. The yolk of the egg of the oviparous animal is 

 certainly not related to the corpus luteum either functionally or an- 

 atomically. Moreover, the egg yolk pigment has been demonstrated 

 by Palmer (1915) to be physiologically as well as chemically identical 

 with at least one, and probably a group of the plant pigments which 

 are known as xanthophylls. Egg yolk xanthophyll is, in fact, a true 

 carotinoid, or mixture of carotinoids, and no further designation 

 appears necessary. 



'The heretofore inexplicable property of being precipitated by mercury salts, ascribed 

 to the luteins by Thudichum, becomes clear only in the light of Palmer's (1914 c) obser- 

 vations that the albumin with which carotin is sometimes associated in the blood serum 

 of animals is precipitated by mercury salts. It is also possible that Thudichum 

 observed the phenomenon of the adsorption of carotin by mercury salts described by 

 Tswett (1906 b). 



