VITAMIN D 295 



factor. Butterfat is richer in fat-soluble A than in the calcium-depositing 

 factor. Cod-liver oil is exceptionally rich in both substances. It has 

 only been found possible up to the present time to demonstrate the 

 differences between these two fats by using diets poor in calcium, for 

 with the low intake of this element there is a correspondingly high 

 requirement of the substance which we have spoken of as a calcium- 

 depositing factor, but which is more than this. It exerts a distinct 

 influence on the anatomic elements of the growing bone and enables 

 the osteoblasts to form approximately the optimum amount of osteoid 

 tissue. It leads to the deposition of calcium phosphate in a degree which 

 is not possible in its absence when the calcium content of the diet is 

 very low. It improves the general well-being of the animals." 



At about the same time Hart, Steenbock and Hoppert (1921) dis- 

 covered through calcium balance experiments with milking and dry 

 goats, the presence of a calcium-conserving factor in cod-liver oil and 

 in green oats and good oat hay ; but not in dry oat straw. This factor 

 in plant tissues, they demonstrated, is distinct from vitamins A, B, 

 or C, and functions in the calcium economy of adults as well as of 

 young. 



Later, in July 1922, Hart, Steenbock, Hoppert and Humphrey com- 

 pared the efficiency of dry and green alfalfa hay in maintaining cal- 

 cium and phosphorus equilibrium in milking cows. Forbes and his 

 coworkers had shown previously that feeding dry alfalfa hay under con- 

 ditions of liberal milk production usually results in a considerable loss 

 of calcium. Hart and his coworkers found that this loss can be pre- 

 vented if the hay has been carefully cured under caps, and can be 

 turned into a decided positive balance if an equivalent amount of fresh 

 alfalfa is fed. They concluded that, "Apparently the question whether 

 positive or negative balances will prevail in liberally milking cows 

 through the use of such an efficient carrier of calcium as alfalfa hay 

 is determined by the quality of the alfalfa hay used. By the term 

 quality, used in this connection, we mean the relative degree of de- 

 struction in the curing processes of the unknown factors affecting cal- 

 cium assimilation." 



Bogert and Trail published, in 1922, two papers relating to the 

 inorganic metabolism of women, in which they reported that the addi- 

 tion of yeast or the substitution of an equal weight of purified butter- 

 fat for purified fat from nut margarine in a diet very low in vitamins 

 exerted a favorable influence- upon the calcium, phosphorus and mag- 

 nesium balances of the subjects studied. 



In August 1922, McCollum and his coworkers furnished explicit 



