324 THE VITAMINS 



cent calcium to A/R of 1.20. This expression serves to magnify 

 differences. 



For several years Osborne, Mendel and Park (1923; Osborne and 

 Mendel, 1927) have been engaged in formulating a "synthetic" diet that 

 will permit the study of changes in the development of the bony struc- 

 ture as a result of alterations in a single factor in the food. Obviously 

 such a diet is of importance in vitamin D studies as well as in other 

 connections. They use purified dietary ingredients and a salt mixture 

 that can be maintained comparable, except for a single element, and 

 which can be altered to make the diet vary in its potential acidity or 

 alkalinity. One of their food formulas furnishes the following in- 

 gredients : edestin 20, starch 75, salt mixture XXX 2.6 parts. Vitamin B 

 is furnished daily in the form of 0.2 gram of dried yeast to which 

 sufficient calcium chloride has been added to maintain the ratio 

 Ca: P: : 1 : 0.5. Vitamin D is furnished daily by means of cod-liver 

 oil ; in experiments that exclude the antirachitic factor the same dose of 

 olive oil is used. Their salt mixture XXX is devoid of calcium and 

 phosphorus and has the following composition : 



Grams Grams 



MgCOs 21.8 Fe citrate 6.34 



Na^COs 30.1 KI 02 



K^COs 118.6 MnSO* 079 



HCl 95.3 NaF 248 



H2SO4 9.2 KsAUCSOOj 0245 



Citric acid. H2O 30.6 



The mixture is neutral. Calcium or phosphorus or both can be added 

 in the form of various salts so as to produce any ratio of Ca : P that is 

 desired. The potential reaction can be varied from alkalinity to acidity 

 by the appropriate selection of the compounds of calcium and phos- 

 phorus added. 



This diet should be useful in the study of many nutritional problems. 

 The vitamin supply, the protein level, the modifying effect of fats and 

 carbohydrates respectively, the potential reaction, the ratio of the bone- 

 forming elements to each other, and the relative "levels" at which they 

 occur in the intake can be independently or conjointly modified. 



They report that numerous experimental obstacles have arisen in 

 connection with what involves primarily the metabolism of calcium and 

 phosphorus in the growing animal. The presence or absence of fats 

 seems to effect a modifying influence. 



By modifying a diet adequate in other respects but free from fat- 

 soluble vitamins to include 20 per cent wheat embryo, 50 per cent hog 

 millet, or 1 per cent alfalfa meal, Soames and Leigh-Clare (1928) found 



