VITAMIN D 323 



Growth. — At one time Steenbock, Nelson and Black (1924) sug- 

 gested that the vitamin D content of food be measured by finding how 

 much will furnish such a sufficiency of vitamin D that irradiation has 

 no further effect upon growth. They stated, "This, however, has its 

 limitations because vitamin A must be present in sufficient amounts to 

 allow normal growth and also because with the introduction of large 

 amounts of such a material as alfalfa the inorganic balance is changed 

 so that ultimately the amount of vitamin required may actually be much 

 less, and with other materials may be greater." 



Composition of Bone. — In other studies involving a quantitative 

 measure for the antirachitic factor, Bethke, Steenbock, and Nelson 

 (1923) used the ash content of bones. They considered the ash content 

 calculated on the basis of dry ether-alcohol extracted bone (femur and 

 humerus) to be more significant than on the "green-bone" basis, "as the 

 bones of animals vary so much in lipoidal and fat content even when 

 taken from animals on the same ration that the accuracy of percentage 

 values is seriously interfered with if omitted." (Cf. Sherman and 

 Stiebeling (1929, 1930) cited briefly below.) 



Dutcher, Creighton and Rothrock (1925) established standards for 

 different ages in their animals on normal, rachitic and irradiated rachitic 

 diets, using the level of inorganic phosphorus in the blood and the per 

 cent of bone ash calculated on the basis of dry extracted femurs. They 

 stated their belief, "that these chemical methods should be very useful 

 in making accurate estimations, in a relatively short time, of the anti- 

 rachitic potency of our common foods. It offers a quantitative method of 

 unusual interest for we should be able to find, by feeding experiments, 

 the minimum amount of any food which will prevent an appVeciable 

 fall in inorganic blood phosphorus or bone ash below the normal level of 

 a normal 40-gram rat or the minimum amount of any food which will 

 bring about normal deposition of mineral matter in bones." 



Goldblatt and Soames (1923b), Chick and Roscoe (1926), and other 

 English workers have used percentage of calcium in dry bone or dry 

 extracted bone as a measure of the influence of the antirachitic fac- 

 tor. Goldblatt (1923) found 20.6 per cent calcium in the bones (dry 

 weight) of animals on a diet containing a satisfactory salt mixture, 

 and furnishing ample fat-soluble vitamins, and 14.6 per cent in those 

 receiving no fat-soluble vitamins, after 7 to 8 weeks on the experi- 

 mental diet. 



Chick, Korenchevsky and Roscoe (1926) suggested the use of "A/R 

 ratio" (ash to organic residue) to express degree of calcification. In 

 their work 17 per cent calcium is equivalent to A/R of 0.90 and 20 per 



