MINERAL METABOLISM 323 



(according to Eona and Takahashi) affect the Ca ion concentration of the 

 blood to any degree. 



Magnesium 



Magnesium has not so far taken on the importance that the other min- 

 erals have in a consideration of mineral metabolism, possibly because 

 the body need is relatively small and always sufficiently covered by the 

 food supply so that the nutritive disturbances which might follow lack 

 of Mg are not observed. Osborne and Mendel found that a diet poor in 

 Mg supported growth of rats as well as one richer in Mg but in the Mg- 

 poor diet they may not have gotten below the minimum requirement The 

 very small amount of Mg in human milk, which is not compensated by 

 a storage in the infant's body as is Fe, leads to the conclusion that Mg 

 needs are at least extremely low. Bertram found that 0.73 per day more 

 than covered the b9dy needs, and resulted in storage of Mg for a few 

 days, after which equilibrium was established. Renvall found a balance 

 established on an intake of about 0.45 g. Mg; on 0.25 g. there was a loss 

 of Mg by the body. Von Wendt(a) found in one case a slight storage on 

 0.20 g. MgO daily and in another a loss of Mg on 0.33 g. Sherman in 

 studies on 150 American dietaries found an average intake of 0.34 g. Mg 

 per day, which probably expresses a little more than the minimum require- 

 ment. Neither Mg (Wheeler) nor Sr (Lehnerdt) can replace Ca physio- 

 logically. 



In bones the amount of Ca is 8 to 9 times that of Mg, in muscle the 

 Mg is 2 to 3 times the Ca, in nerves the amount of Mg is about twice that 

 of the Ca. In fasting the elimination of Ca is 3-4 times that of Mg, indicat- 

 ing a catabolism of both bone and body protein. 



Absorption of Mg is similar to that of Ca, though it seems to suffer less 

 interference by the presence of other substances. Its distribution in the 

 urine and feces is subject to the same variations as that of Ca under similar 

 conditions though a larger proportion of the total Mg is urinary ; urinary 

 Mg is usually lower than urinary Ca (Givens(fr) ). The ingestion of large 

 amounts of Mg salts has been found to increase the Ca elimination, but Mg 

 elimination seems to be independent of Ca ingestion (Malcolm; Hart and 

 Steenbock(a). Fats and carbohydrates decrease Mg retention in infants 

 (Birk). 







Phosphorus 



None of the other inorganic elements has so wide a distribution in 

 various forms in the animal body as has phosphorus. Its importance in 

 life processes is reflected in the great volume of literature that has been 

 contributed upon its occurrence, its nutritive history and its functions. 



