BIOI,OGICAI, PROPERTIES OF BUTTER 571 



method of chemical analysis, their presence has only become 

 recognized by means of experimental feeding trials with young 

 animals. 



These feeding trials, largely though not exclusively con- 

 ducted with young white rats, showed that when the animals 

 were put on an artificial diet, containing all the chemical ele- 

 ments necessary for nutrition, both for maintenance and for 

 growth, such as protein, carbohydrates, fats and mineral salts, 

 but in which the fat part of the ration consisted of a vegetable 

 oil or of lard, the rats would after a brief period cease to grow, 

 so that they rarely attained more than two-thirds of the normal 

 growth of fully grown rats. As this diet was continued they 

 would lose weight and gradually develop sore eyes which culmi- 

 nated in blindness and ultimate death of the rats. When, before 

 the death of the rats, a portion of the animal or vegetable fat in 

 the ration was replaced by butter or butterfat, they recovered 

 from their disease, gained in weight and resumed their normal 

 growth. 



Fat-Soluble A. Further experiments in which the pure 

 butterfat was separated from the butter, and the butterfat in- 

 stead of the butter was used to replace a part of the lard in the 

 feed ration, yielded identically the same results as in the case 

 of butter, showing therefore that this growth-promoting and 

 curative property of the butter is located in the butterfat. 

 Being soluble in the butterfat, McCollum gave this unknown 

 substance the name fat-soluble A. 



Fat-Soluble A Present in Liquid Portion of Butterfat. 

 Osborne and Mendel succeeded in concentrating the fat-solu- 

 ble A substance contained in butterfat by .fractional crystalliza- 

 tion of the fat from alcohol. They found that the fat-soluble A 

 substance remains in .the mother liquor, or oily portions, those 

 portions which have a low melting point, while the other por- 

 tions, those that have a high melting point, proved entirely 

 ineffective. This fact assists in explaining why beef fat, which 

 also contains small quantities of this substance, is much less 

 effective in its growth promoting powers than the butterfat. The 

 liquid portion in the beef fat is relatively small. 



Fat-Soluble A Not Affected by Pasteurization, Neutraliza- 

 tion or Age. Additional experiments showed that the fat-soluble 



