272 THE VITAMINS 



exclusively dependent upon it, because of stores in the body. The 

 presence of an abundance of vitamin A in the grasses on which dairy 

 cows are pastured in summer and in the hays fed in winter is an 

 important factor in ensuring that the milk produced by the cow is 

 rich in vitamin A at all times of the year. A factor of safety in main- 

 taining the vitamin A value of milk is the fact that the store of this 

 vitamin carried in the body of the cow is undoubtedly drawn upon to 

 keep up the normal concentration in the milk in case of fluctuations in 

 the supply received in the feed. 



Of interest in this connection is the observation of Drummond, 

 Coward and Watson (1921) that colostrum has a much higher con- 

 centration of vitamin A than the later milk. They are inclined to regard 

 this higher value of colostrum as an indication of a mobilization of the 

 reserves of the mother since it does not appear to be proportional to 

 the fat content. "It is again interesting to recall that there is also a 

 partial mobilization of the lipochrome pigments of the mother's body 

 fat for the production of colostrum which normally contains a much 

 higher concentration of those coloring substances than the later milk." 

 A similar relation between vitamin A and the lipochrome pigments is 

 suggested in the apparent tendency reported by these investigators for 

 milk from cows of the Jersey and closely related breeds to be richer 

 in vitamin A than that of Shorthorn or Black Angus. As a possible 

 explanation, it is suggested that cows of the former breeds may have 

 a higher storage capacity for vitamin A similar to their higher capacity 

 for storing pigment. 



The average vitamin A content of fluid milk is about 2 units per 

 gram (or about 2,000 units per quart) ; that of condensed and evapo- 

 rated milks about 4 units per gram, and of dried whole milk about 16 

 units per gram. To what extent milk can be enriched in vitamin A by 

 increasing the amount of this factor in the food of the cow is still 

 a matter of investigation. 



So far as the writers are aware, there is no conclusive evidence as 

 to how the vitamin A content of milk is divided quantitatively between 

 its fat globules and its aqueous phase. The observations noted in the 

 . first edition of this monograph are now beheved to have overestimated 

 the proportion contained in skim-milk as compared with whole milk 

 and butterfat. Crawford, Golding, Perry and Zilva (1930) believe that 

 all the vitamin A (and D) of milk is in the fat. 



Butter appears usually to contain about 30 to 50 units of vitamin 

 A per gram, ranking in richness, weight for weight, with egg yolk and 

 fresh spinach. Variations of vitamin A value of milk due to changes 



