VITAMIN A 271 



ficient in vitamin A. The blood of the rats used in the study of the 

 quantitative distribution of the vitamin contained from 1 to 2 units 

 per gram. Judging from the results of that study and reports from 

 other laboratories, kidney may be estimated to contain from 8 to 10 

 units per gram, lung from 10 to 15 and liver from 5 to 140 units per 

 gram. 



Some of the animal fats and oils are rich sources of vitamin A. 

 Cod-liver oil has long been known to contain high concentrations. 

 Indications are that storage in a cool dark place is not attended by 

 marked destruction. Storage in warm light places for varying lengths 

 of time has in some instances been reported to result in over 95 per 

 cent destruction of the vitamin. Other fish liver oils which contain 

 similar concentrations of the vitamin are those from burbot, coalfish, 

 dogfish, haddock, hake, pollock, and topefish. Seal and whale oil are 

 fairly rich sources of vitamin A. Fats of beef, dog, horse, mutton, pig, 

 poultry and wool have shown measurable amounts of vitamin A. Lard, 

 which usually seems lacking in the vitamin, has at times shown de- 

 tectable quantities. Whole small fish, which serve as food for the cod 

 are reported to contain from a few to approximately 500 units per gram. 



Eggs are an important source of vitamin A. The vitamin is con- 

 tained essentially in the yolk of the &gg and the concentration depends, 

 to an extent not yet fully determined, upon the food of the fowl. 

 Undoubtedly the fowl depends upon its food for the vitamin A which 

 the tgg contains; but to what extent a shortage of this vitamin in the 

 food results in the production of vitamin-A-poor eggs, as against a 

 simple diminution of ^gg production, remains to be investigated in 

 detail. There is little doubt that tgg yolk is a more constant source of 

 vitamin A than is liver, which alone among animal body tissues 

 approaches it in richness in this vitamin. The egg as a whole may be 

 expected to contain about 15 to 20 units of vitamin A per gram; and 

 the yolk about three times this concentration. 



Milk is also a rich source of vitamin A. While the number of 

 units per gram is not conspicuously high, the extent to which milk 

 enters into the well-planned dietary makes it one of the most important 

 sources of this substance. It was largely because of their importance 

 as sources of vitamin A as well as of calcium that milk and green 

 vegetables were designated by McCollum as "protective foods," al- 

 though their newly discovered vitamin G values will further strengthen 

 this classification. 



In the case of milk, the vitamin A content is influenced by the 

 abundance of the supply contained in the feed; but not directly and 



