CAROTIN, THE PRINCIPAL YELLOW PIGMENT OF MILK FAT 437 



a very abnormal composition which is characterized by a very low 

 fat percentage and a very high protein content, the largest proportion 

 of which is albumin. Unpublished data are at hand which show a 

 composition of some colostrum milks of 1.3 per cent fat and over 4.5 

 per cent albumin. When it is considered that the carotin is carried 

 by the blood in combination with an albumin, and when it is also 

 taken into account that the source of the lactalbumin is undoubtedly, 

 at least partially, the serum albumin, a most plausible explanation 

 of the high color of colstrum milk fat is at once apparent. It is also 

 apparent that this high color will continue until the milk has reached 

 a normal composition or until the blood supply is depleted. That 

 this will occur regardless of breed is also readily explained since data 

 show that the maximum color of the blood serum does not materially 

 differ with different breeds. 



DISCUSSION OF RESULTS. 



The results of the foregoing studies in regard to the yellow 

 lipochrome of the blood serum of the cow do not require any extended 

 discussion. Following the interesting discoveries set forth in the 

 preceding papers in regard to the nature of the pigments of milk 

 fat and body fat and their simple physiological relation to the carotin 

 and xanthophylls of the food which the cow receives, it was not sur- 

 prising to find that the hitherto practically unknown lipochrome of 

 the blood serum of the same animal is also chiefly carotin and bears 

 the same relation to the food as the milk fat carotin. We are thus 

 able to establish the connecting link between the food carotin and 

 the carotin of the milk fat, body fat carotin, corpus luteum, etc., of 

 the cow. 



One of the most important results of this study was the dis- 

 covery that the carotin is not transmitted to the milk glands and body 

 cell from the food by means of simple solution in the blood serum, 

 but is on the other hand carried through the body in combination 

 with an albumin of the serum. 1 This fact is undoubtedly of con- 

 siderable importance in connection with the entire phenomenon of 

 the pigmentation of the milk fat. It may be safely predicted that 

 all the factors which surround this phenomenon are in some way 

 dependent upon this fact, and all these factors will not be known until 

 it is clearly understood what part this caroto- (or luteo-) albumin 



1. Incidentally this discovery has resulted in the addition of a new 

 chromoprotein to the list of conjugated proteins. This is itself of consider- 

 able physiological interest. 



