CALCIUM 41 



calcium which is combined with casein in milk is of superior nutritive 

 value to that which is present in the milk from the beginning in the 

 form of diffusible inorganic salts of lime. An experiment which used 

 to be frequently quoted in support of this view was that of Lunin's; 

 who fed six mice upon a mixture of casem, fat and cane-sugar plus the 

 inorganic salts contained in milk. These animals lived respectively 

 twenty, twenty-three, twenty-nine, thirty and thirty-one days; where- 

 as two mice of the same age fed entirely upon whole cow's milk for a 

 period of seventy-five days remained in good health at the end of the 

 experiment. In the first experiment the inorganic bases were all com- 

 bined with inorganic acids to form diffusible and ionizable salts, where- 

 as in the second experiment the lime, at least, was combined with 

 casein. Hence, it was argued, lime in the inorganic form did not fulfil 

 the necessary requirements of the animals. 



This experiment might easily have been seen from the first to be 

 inconclusive, for natural milk and an artificial mixture such as that 

 prepared by Lunin must obviously differ in many particulars besides 

 the single particular of the diffusibility of the calcium. But in the 

 light of our more recent accessions of knowledge concerning the nutri- 

 tion of animals it has become quite clear that Lunin's experiment 

 bears a very different interpretation to that which was originally put 

 upon it. 



We know now, thanks to researches which will be detailed in a later 

 part of the work, that besides a sufficiency of proteins, fat and carbo- 

 hydrates, any diet which is to maintain animals in health for a con- 

 siderable period must contain other essential constituents which are 

 present in milk or in animal tissues in minute amounts. These con- 

 stituents fall into two distinct classes, at least, and possibly as our 

 knowledge increases will be found to be more numerous and more 

 diverse in their chemical characteristics than we at present realize. 

 The two classes of these "accessory foodstuffs'* which are at present 

 recognized, however, are in the first place the vitamines, which are 

 nitrogenous, water-soluble substances and in the second place a group 

 of substances which are commonly found associated with animal fats, 

 but are generally absent from vegetable fats. Thus Hopkins has 

 found that if animals be fed for a considerable period on milk-salts, 

 casein and milk-sugar they will not survive, while the addition of a 

 small amount of butter suffices to render the diet adequate for the 

 needs of the animals. 



In the light of these facts it will readily be seen that Lunin's experi- 

 ment does riot bear on the question of calcium-nutrition at all, but 

 rather on the question of accessory .organic foodstuffs. Furthermore, 

 recent experiments have shown that the cane-sugar employed by Lunin 

 in his artificial mixture is not by any means a sufficient substitute 

 for milk-sugar in the dietary of young animals. 



There is thus no evidence whatever that the two forms of lime in 

 milk are not equally available and useful to the suckling, as we should 



