GROWTH 419 



It has been maintained, principally on the basis of Soxhlet's 

 experiments on calves (493), that the availability of the ash 

 ingredients of milk, and particularly of its calcium and phos- 

 phorus, is especially high. The percentages retained in the 

 body on the average of the five trials were : 



Total ash 53.0 



Potassium 20.7 



Sodium 29.1 



Calcium 97.0 



Magnesium 30.5 



Phosphorus 72.5 



Chlorin 3.8 



Neumann's experiments with somewhat older calves (493), 

 however, render it evident that the cause of the high retention 

 of calcium and phosphorus was the large demand for these 

 elements in the body. It can hardly be supposed that these 

 elements are less assimilable in the skim milk used in Neumann's 

 experiments, yet the percentage retention was scarcely more 

 than one-half as great as in Soxhlet's experiments, viz., in the 

 experiments on skim milk alone. 



The older animals obviously required less of these elements 

 and therefore excreted the excess, the phosphorus in the urine 

 and the calcium in the feces. 



Lehmann's and Weiske's experiments (493) with older calves 

 on mixed rations showed a percentage availability of the phos- 

 phorus and calcium fully as great as that observed for skim 

 milk in Neumann's experiments, and here too the natural con- 

 clusion is that the demand for these elements in the body, 

 rather than any lower availability per se, is the cause of the less 

 assimilation. It is well established that the inorganic phos- 

 phates may be quite completely assimilated, and Fingerling 1 



1 Landw. Vers. Stat, 79-80 (1913), 847 J 86 (1915), 75- 



