326 THE VITAMINS 



maximum values obtainable in rats of the same age and on the same 

 basal diet with (1) no added vitamin D, and (2) with an ample supply, 

 respectively. Their basal diet consisted of : Casein, fat-soluble vitamin- 

 free, 18 per cent; salt mixture (Osborne and Mendel), 4 per cent; dry 

 brewers' yeast, 10 per cent ; sodium chloride, 1 per cent ; powdered dry 

 spinach, 1 per cent ; cornstarch, 66 per cent. This diet contains enough 

 vitamin A to permit rats reared under their conditions to make very 

 good growth when vitamin D is liberally supplied. 



In the course of these experiments data were accumulated by the 

 use of which the degree of calcification (ossification) was expressed in 

 each of the following several terms : percentage of ash, or of calcium, 

 in the fresh bone ; percentage of ash, or of calcium, in the dried, alcohol- 

 ether-extracted bone ; and/or the ratio of the ash to the organic residue 

 of the dried extracted bone. 



From their data it appears that all of these suggested criteria are 

 of about the same order of accuracy, and they recommend the use of 

 the percentage of ash, or of calcium, in the fresh bone as the criterion 

 for the degree of calcification. 



They found both growth and calcification improved by supple- 

 mentary graded portions of vitamin D, but the calcification appeared 

 to be more regularly aflfected. 



Mineral Balance. — Boas (1926) studied the antirachitic value of 

 spinach by carrying out direct metabolic experiments on rats, comparing 

 the influence upon retention of calcium and phosphorus of daily addi- 

 tions to a diet deficient in fat-soluble vitamins, of cod-liver oil and fresh 

 green winter spinach leaves. 



Hart, Steenbock and coworkers (1923) have repeatedly found that 

 balance experiments on goats could measure the eflfect of the anti- 

 rachitic factor and Sjollema (1923) has made use of such experiments 

 with rabbits, but the great labor involved in such studies, and the high 

 percentage errors likely to be encountered have deterred most workers 

 from using balance studies with small animals to measure the vitamin 

 D content of foods. 



Reaction of Intestinal Contents. — Jephcott and Bacharach reported 

 (1926) that they had developed a rapid and reliable test for vitamin D 

 based on the observation of Zucker and Matzner to the effect that rats 

 kept on a typical high-calcium low-phosphorus rachitogenic diet develop 

 marked fecal alkalinity, and that the administration of an antirachitic 

 to rats causes the feces again to become acid. This method, they say, is 

 satisfactory only when the test material contains a high concentration 

 of vitamin D, as cod-liver oil, or (in some cases) if the test food can 



