BIOLOGICAL RELATIONS BETWEEN CAROTINOIDS 197 



determination of the relative solubility of their bile on carotin and 

 xanthophylls might lead to suggestive results. No fact has as yet 

 come to light, however, which offers any reasonable basis upon which 

 one can construct an explanation of the rather astonishing divergence 

 between this species and the mammals with respect to the class of 

 carotinoids winch predominate in the chromolipoids which color the 

 body tissues. 



Summary 



The demonstration of the possibility of a general biological rela- 

 tionship between animal chromolipoids and plant carotinoids is a 

 recent achievement. Such a relationship was suggested by earlier 

 workers in isolated cases, but even the chemical identification of cer- 

 tain of the animal lipochromes with plant carotinoids did not suggest 

 to Willstatter and his pupil Escher their possible origin from plant 

 pigments. 



Of the earlier investigators Krukenberg and Zopf saw no evidence 

 of such a biological relationship. Miss Newbigin concluded that such 

 a relation existed in specific cases but was not general. Poulton, how- 

 ever, decided that for caterpillars the yellow pigment is derived from 

 "xanthophyll" and the green from chlorophyll. 



In addition to Poulton's work, the earlier experiments demonstrating 

 that plant carotinoids can be transferred to animal tissues included 

 Saucrmann's (1889) coloring of the feathers of canary birds and fowls, 

 and the egg yolks of the latter, with red pepper pigment. The experi- 

 ments should be repeated, however, because the results present the 

 apparent anomaly that lycopin (which is apparently the red pepper 

 pigment), the isomer of carotin, is assimilated by the fowl while 

 carotin is absorbed only in traces under the most favorable conditions. 



Since these earlier studies Palmer (1914, 1915, 1919) has demon- 

 strated that the carotin of the butter fat, adipose tissue, blood serum, 

 skin secretions, etc., of cattle is biologically derived from the food; 

 that a similar relationship exists between the xanthophyll of egg yolk 

 and fowl tissues and plant xanthophyll; that while there is not an 

 absolute exclusion of xanthophyll by the cow or carotin by the hen, 

 the occurrence of a predominating type of carotinoid in each of the 

 two species is not due to the power of the animals to convert one 

 type of pigment into the other; and that the pigments of human milk 

 fat (and presumably of human tissues in general) may contain either 

 carotin or xanthophylls or both. 



