BIOLOGICAL CLASSIFICATION OF FfJODS 47 



In a mixed diet, there is usuall^^ but not al\va}'s, a sufficiency 

 of the compounds of the different elements mentioned. W'e 

 quote Sherman upon this point: " There must also be main- 

 tained in the body a proper balance between sodium and calcium 

 (the metal of lime). For example, the rhythmical contraction 

 and relaxation of heart muscle, which constitutes the normal 

 beating of the heart, is dependent upon this muscle being bathed 

 by a fluid containing the proper concentration and quantitative 

 proportions of sodium and calcium. Calcium is not always suf- 

 ficienth' abundant e\'en when the food is freely chosen; hence the 

 richness of a food in calcium is a factor affecting its value. "^ 

 IMcCollum and Simmonds found as a result of their experiments, 

 " that the deficiency in mineral elements in wheat and other seeds 

 is limited to three elements, calcium, sodium and chlorine."^ 



The ash of milk is present in hberal quantit}', is of high qual- 

 ity and well balanced, and is rich in its lime content as a source 

 of calcium. There is more lime in a pint of milk than in a pint of 

 hmewater. 



Two Unidentified hut Essential Food Substances — One of These 

 in Milk'fat but not in Ordi)iary Fats 



There are, in association with some of the foodstuffs, sub- 

 stances which have not as yet been identified chemically, pos- 

 sibly on account of the minute quantities in which the}- are 

 present; and }'et obserA-ation, in feeding experiments, has shown 

 that they are indispensable. If these are absent from their 

 foods, animals will neither grow nor retain vigor. 



As early as igo6, Hopkins of Cambridge (England) showed 

 conclusively that on an apparently complete food made up of 

 purified proteins, ordinary fats, carbohydrates and salts young 

 rats would not grow, but that when a A-ery small amount of milk 

 was used — enough to make up about 4 per cent of the dr)' matter 

 of the food — growth became entirely satisfactory. This led him 

 to conclude that there were present in milk unidentified food 

 substances which he termed " accessory " articles of the diet. 



' Food Products, pp. 19 and ^o. 



^The Newer Knowledge of Nutrition, p. 23. 



