Chapter VII 



Biological Relations between Plant and Animal 



Carotinoids 



The origin of color in animals, when considered by and large, has 

 been, until recently, practically an unexplored field. So far as the 

 colors which might be due to carotinoids or related pigments are con- 

 cerned no systematic study of their possible biological relationship to 

 plant pigments of similar color was undertaken previous to the inves- 

 tigations by Palmer and Eckles, published in 1914. A few close 

 students of the subject have, indeed, suggested such a relationship in 

 isolated cases, which are mentioned below, and there are also certain 

 isolated observations which support the idea. It is a striking fact, 

 however, that so little experimental work had been done in this field 

 that even the chemical identification of certain of the animal lipo- 

 chromes with plant carotinoids by Willstiitter and Escher (1912) 

 and by Escher (1913) apparently raised no query in their minds as 

 to their possible origin from the plant pigments. For example, 

 Escher, in concluding the paper on corpus luteum carotin remarks, 

 "What this unsaturated terpene hydrocarbon, carotin, which is so 

 widely distributed in the plant world, is doing in such an important 

 gland as the corpus luteum, can not even be conjectured at present, 

 there is nothing in the literature to establish whether it is a sub- 

 stance produced from one of the specific gland cells, or is only a 

 pigment which has been resorbed by the cells from the blood ex- 

 travates." It is clear, also, that Escher saw no biological relation- 

 ship between the xanthophyll of the egg yolk and plant xanthophylls, 

 for he expresses the view that, "the oxygen-containing lutein 

 (C 40 H 56 2 ) in the yolk of eggs plays the part of an atavistic plant 

 respiratory pigment for the formation of hemoglobin in the embryo." 

 It is true that when Fischer and Rose (1913) isolated carotin from 

 the gall stones of cattle they were unable to agree with Escher's con- 

 clusion and suggested, rather, that the carotin in the cow's body 

 probably comes from the food. In reality, however, Escher's general 



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