CAROTINOIDS IN THE VERTEBRATES 151 



luteum of the cow. Although the general relation of this pigment to 

 other yellow animal pigments, and even to certain of the plant 

 chromolipoids was recognized by a number of subsequent investigators, 

 its identity as rarotin was not established until the work of Escher 

 (1913). The character of the corpus luteum pigment in other mam- 

 mals and in man has not been determined. Carotinoids are absent 

 entirely in the case of the so-called yellow bodies on the ovaries of 

 swine. 



The existence of a chromolipoid in the blood serum of certain 

 mammals was known as early as 1835. Krukenberg (1885a) first 

 succeeded in isolating the pigment (using ox serum) and classified the 

 pigment as a lipochrome. The relation of the pigment to the caro- 

 tinoids which characterize other mammalian tissues was not estab- 

 lished until the work of Palmer and Eckles (1914c). The chromo- 

 lipoid of cattle and horse serum is carotin, but in man it may be either 

 carotin or xanthophyll. Carotin, when present, is frequently, if not 

 always, bound to colloidal serum albumin, but this does not appear 

 to be the case for xanthophyll. Carotinoid is not always the sole 

 pigment in blood serum, bilirubin also being present at times, particu- 

 larly in the case of man and the horse. The blood serum of a num- 

 ber of mammals is almost or entirely devoid of carotinoid pigment 

 under all conditions, e.g., swine, sheep, goats, dogs, cats, guinea pigs 

 and rats. This is also true for the new-born animals of the species 

 whose serum is pigmented in later life. 



The chromolipoid of milk fat is the carotinoid which characterizes 

 the blood plasma of the animal, as shown by the author's studies. 

 Carotinoid coloration of milk fat is not, however, universal among 

 mammals, pigmentation being determined by the kind and amount of 

 carotinoid carried by the blood. 



The chromolipoids of the adipose tissue, internal organs, nerve cells 

 and skin of mammals are the carotinoids which characterize the blood 

 serum, only those animals whose blood serum is normally pigmented 

 with carotinoids depositing the pigments in their body tissues and 

 organs. 



The more frequent observation of an epidermal carotinoid coloration 

 among diabetics than among well persons is due largely to the vege- 

 tarian character of the diet in diabetes, from which the pigments are 

 derived. The author suggests, however, that the phenomenon is due 

 also, in part at least, to the lowered oxidative tone of the body in this 



