Chapter IV 

 Carotinoids in the Vertebrates 



It is by no means a new idea that certain pigments, widely dis- 

 tributed among animals, resemble closely in their chemical and physi- 

 cal properties, as well as in color, the pigments of the vegetable king- 

 dom which were considered in the preceding chapters. This point 

 was brought out in Chapter I. The demonstration of a general biologi- 

 cal relationship of these animal pigments to the plant carotinoids is, 

 however, comparatively recent. It is because of this relationship 

 that one is justified in considering the carotinoids of plants and ani- 

 mals in one treatise. The development of this idea and the experi- 

 mental justification for it are reserved for presentation in a later 

 chapter. It is accordingly necessary to anticipate this discussion at 

 this point and to review the evidence for the distribution of the caro- 

 tinoids among animals without having first justified the basis for 

 this distribution. The reader is therefore asked to assume for the 

 moment that the yellow to orange-red animal pigments which have 

 been most commonly called lipochromes are in all probability true 

 or modified plant carotinoids. For certain of the higher animals 

 proof has been furnished -that their lipochromes are true carotinoids. 

 but this knowledge does not as yet extend very far down the scale 

 of animals. However, the thread is picked up again for certain of 

 the lower animals so that it does not require a difficult stretch of 

 imagination to fill in the gap, wide as it is indeed admitted to be. 



Carotinoids in Mammals 



Corpus luteum. Bearing in mind that carotin was the first veg- 

 etable chromolipoid discovered, it is an interesting fact that the first 

 mammalian chromolipoid to be isolated in crystalline form likewise 

 eventually proved to be carotin. The pigment referred to is that of 

 the corpus luteum of the cow, first described by Piccolo and Lieben 

 (1866) and a little later, apparently independently, by Holm (1867). 

 As already mentioned in Chapter I, the former called the pigment 



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