224 THE VITAMINS 



articles in certain foodstuffs which are essential for normal growth for 

 extended periods." 



Similar conclusions published by Osborne and Mendel (1913) dur- 

 ing the same summer were arrived at from an attempt to explain the 

 great superiority of diets employing milk over purely artificial food mix- 

 tures or even mixtures containing protein-free milk. A mixture of milk 

 powder 60, starch 12, and lard 28 per cent proved to be adequate for 

 growth and maintenance while "protein-free milk" food consisting of 

 protein in the form of edestin or casein 18, starch 26, lard 28, and "pro- 

 tein-free milk" 28 per cent failed to support growth for more than about 

 100 days. The essential difference evidently lay in the absence from 

 the protein-free milk foods of those components of milk which are sepa- 

 rated in the process of centrifugation. This led to the substitution for 

 part of the lard in the protein-free milk food of a corresponding 

 quantity of butter fat, a change which brought about prompt recovery 

 and rapid growth of the experimental animals and which justified the 

 authors in concluding: "It would seem, therefore, as if a substance 

 exerting a marked influence upon growth were present in butter, and 

 that this was largely, if not wholly, removed in the preparation of our 

 natural 'protein- free milk.' Whether or not the latter is wholly deficient 

 in this substance can not be determined as yet from any data we possess. 

 It is true that young rats are able to make very considerable growth 

 when fed on the natural 'protein- free milk' diet, but possibly this is 

 accomplished at the expense of some reserve substance stored in the 

 cells of the young animal." The ability of the animal body to store the 

 fat-soluble vitamin, thus early suggested by Osborne and Mendel, has 

 proven to be a matter of much importance. 



Further study by Osborne and Mendel on the influence of butterfat 

 on growth, reported later in the same year (1913a) showed that the 

 active ingredient was contained in the clear fat fraction of butter, was 

 essentially free from nitrogen and phosphorus and devoid of any ash- 

 yielding material, and evidently not destroyed when steam was passed 

 through the melted butterfat. In discussing the nutritive superiority of 

 butterfat over lard, the authors note at this time that failure at certain 

 periods of the year, particularly in the summer months, to secure satis- 

 factory growth on dietaries which had proved adequate at other times 

 could be averted by the addition of butterfat to the usual protein- free 

 milk food mixtures and further that a "type of nutritive deficiency 

 exemplified in a form of infectious eye disease prevalent in animals 

 inappropriately fed is speedily alleviated by the introduction of butterfat 

 into the experimental ration." This characteristic eye condition (Fig. 8) 



