VITAMIN A 273 



in the food of the cow must result in corresponding variations in the 

 butter made from the milk ; and to this is to be added as a further 

 cause of variation in butter, the possibility of deterioration in vitamin 

 value of the cream or butter under industrial manipulation or storage. 

 It is believed that under good conditions there should be but very little 

 loss from this cause. 



Drummond, Coward and Watson (1921) from an extensive exam- 

 ination of storage butter concluded that the season at which the butter 

 is placed in storage, i.e., the feed of the cows at that season, is a more 

 important factor in determining the value of the storage butter as a 

 source of vitamin A than the length of time the butter remains in 

 storage, provided undue exposure to air is prevented and other condi- 

 tions are good. As, under present conditions, by far the largest part 

 of the butter placed in storage is that produced when the cows are on 

 green pasture and are consequently giving a greater yield of butter of 

 superior quality, and as it is kept in air-tight casks or tins during 

 storage, it seems reasonable to assume that such butter will usually be 

 scarcely less rich in vitamin A than fresh butter as obtained the year 

 round. The development of acidity in butter may occur without appre- 

 ciable loss of vitamin A if oxidation is prevented, while in so far 

 as the process of renovating rancid butter offers opportunity for oxida- 

 tion it may entail sufificient losses of vitamin A to render the product 

 of materially less value in this respect. 



Of interest in this connection is the statement made to one of the 

 writers by an expert judge of butter ("butter taster") that in the 

 winter months storage butter is to be preferred, on account of its 

 summer flavor, to much of the fresh butter obtainable at the time. 



Relation to Nutrition and Health 



Some of the effects of a lack of sufficient vitamin A in the diet may 

 now be summarized briefly as a basis for our consideration of the 

 broader significance of this vitamin in relation to normal nutrition and 

 the ability to resist disease. 



When a diet lacking vitamin A but adequate in all other respects 

 is fed to a young growing rat, growth may cease, or continue slowly, 

 or may continue for as much as 10 weeks at a normal or nearly normal 

 rate, depending upon the store of vitamin A in the body of the experi- 

 mental animal at the beginning, and the amount of the experimental 

 diet eaten. Under favorable conditions growth continues for some time 

 at a nearly normal rate (as indicated by the curves shown in Fig. 10 

 above) during which time the surplus of vitamin A possessed at 



