128 CAROTINOIDS AND RELATED PIGMENTS 



success was attained only by repeated extractions of the serum with 

 amyl alcohol. The writer's study of blood serum pigments of cattle 

 has shown that this difficulty is readily explained. When the chromo- 

 lipoid present is carotin, the pigment is physico-chemically attached 

 to serum-albumin. Alcohols have a greater attraction than pigment 

 for the colloidal protein and thus replace it. Fat solvents will then 

 extract the pigment, petroleum ether being the best solvent to use. 

 Krukenberg's observations of the pigment isolated by him from ox 

 serum were confined to solubility properties in the lipochrome sol- 

 vents, the color reactions with concentrated H 2 S0 4 and HN0 3 , and 

 the spectrum bands of the pigment. Positive identification as a lipo- 

 chrome was secured in each case. Krukenberg was careful to recog- 

 nize that pronounced spectroscopic differences among lipochromes 

 indicated the existence of more than one individual in his lipochrome 

 group. On these grounds he was led to conclude that the blood serum 

 pigment of the ox is probably identical with the lutein of the corpus 

 luteum, whose spectrum properties had been previously pictured by 

 Kiihne. The additional interesting observation was made that the 

 fresh serum itself showed the spectrum bands, although shifted con- 

 siderably towards the red end of the spectrum from their position in 

 chloroform or ether. The writer was unable to verify this for a speci- 

 men of human blood serum which proved to be rich in carotin. 

 Although Krukenberg made no attempt to identify the pigment with 

 any of the vegetable lipochromes with which he was familiar, his 

 graphic representation of the spectrum of the cattle serum pigment 

 shows it to be identical with that of carotin. Krukenberg had no 

 explanation to offer for the occurrence of the pigment in the blood. 

 He was opposed to the view that it originated from hemoglobin, but 

 nevertheless saw an analogy between the simultaneous occurrence of 

 lipochrome with the respiratory pigment of both plants and animals. 

 Van den Bergh and Snapper (1913) confirmed the general observa- 

 tions of Krukenberg regarding the properties of the pigment of cattle 

 serum. In addition, they noted traces of bilirubin in the serum and 

 proposed an interesting test for the presence of both lipochrome and 

 bilirubin in blood serum based on their observation that the lipo- 

 chrome of cattle serum is precipitated with the proteins when two 

 volumes of 95 per cent alcohol are added to one volume of serum 

 while bilirubin remains in the supernatant fluid when the precipitated 

 proteins are centrifugalized. Definite identification of the lipochrome 

 of cattle serum as carotin was made by Palmer and Eckles (1914c) 



