CAROTIN, THE PRINCIPAL YELLOW PIGMENT OF MILK FAT 



417 



calcium carbonate. A detailed description of these properties when 

 applied to both the plant carotin and xanthophylls and the pigments 

 of milk fat, body fat, corpus luteum and skin secretions of the cow 

 was given in the two preceding bulletins 1 of this series, and need not 

 be repeated here. The measurements of the spectroscopic absorption 

 bands of the carotin and xanthophylls which are used for comparison 

 were made according to an arbitrarily fixed and standard scale. It 

 may not be out of place therefore, to repeat here a table which was 

 given in the paper immediately preceding this one, showing these 

 standard measurements. This table is given below as Table I. The 

 measurements in carbon bisulphide solution only are given. 



TABLE No. 1. SPECTROSCOPIC STANDARDS OF CAROTIN AND XANTHOPHYLLS. 



METHODS OF ISOLATION. 



The study of the blood serum lutein required considerable pre- 

 liminary study of methods of isolation. The amyl alcohol method of 

 Krukenberg 2 was not considered suitable on account of the high boil- 

 ing point of the solvent. The method used by Schunck 3 seemed to be 

 much better suited for the work. He precipitated the proteins from 

 the serum with alcohol, and as the proteins carried down the lutein he 

 was able to isolate it by extracting the precipitated proteins with boil- 

 ing absolute alcohol. Preliminary investigations of the blood serum 

 lutein using Schunck's method showed, however, that it was applicable 

 only to serum free from dissolved red blood corpuscles. When 

 hemoglobin was present it was always carried down with the protein 

 and some of the red color dissolved in the subsequent alcohol extract. 

 In addition, the method did not seem to be a quantitative one, some of 

 the lutein invariably being found in the dilute alcoholic filtrate from 

 the precipitated proteins. These investigations showed however, that 

 in every case both petroleum ether and carbon bisulphide almost quanti- 



1. Research Bulletins Nos. 10 and 11, Missouri Agr. Exp. Sta.; also Jour. 

 Biol. Chem. 17, pp. 191, 211 (1914). 



2. Loc. cit. 



3. Loc. cit 



