438 FORBES! MINERAL ELEMENTS IN NUTRITION 



the incomplete character of its largest protein constituent, 

 zein. The only effects which can safely be attributed to the 

 mineral constituents of corn are those affecting the skeleton. 



In one experiment corn alone was compared with corn supple- 

 mented by soy beans, linseed oilmeal, wheat middlings, tankage, 

 and skim milk. The rations of corn alone and of corn and 

 soy beans produced the least bone. The rations of corn supple- 

 mented by tankage and skim milk produced the most bone. 

 Rations of cereals or other seeds will not produce normal growth 

 of bone in swine. These facts depend directly on the content 

 of these foods in the chemical elements which compose bone. 



The proportion of calcium, magnesium, and phosphorus in 

 the bones tends strongly to remain constant, but may be modi- 

 fied to a certain extent by the limitations of the food. The 

 amounts of these elements in the bone, however, are susceptible 

 of much greater modification through the composition of the 

 food. Bone meal, when added to a ration which is low in cal- 

 cium and phosphorus, will greatly increase the ash and strength 

 of the bones. The change in external dimensions is slight, but 

 increase in the density and thickness of the walls of the bones 

 may proceed indefinitely. The readiness with which minerals 

 may be deposited in the bones, the lack of a definite upper limit 

 of such deposit, and the readiness with which these minerals 

 may be withdrawn constitute the skeleton a true store of min- 

 eral nutriment. 



We have not been able by any method of feeding, in confine- 

 ment, to produce bones as strong as are the bones of pigs raised 

 on pasture. It seems quite possible that exercise, as well as 

 food, has its effect to strengthen the bones through inducing 

 an added avidity of the osteogenic cells for bone salts. 



In a metabolism investigation with swine five pigs, all from 

 the same litter, were taken through eight 10-day collection 

 periods separated by 7-day intervals. The feeds, as in the 

 experiment last mentioned, were corn alone, compared with 

 corn supplemented by soy beans, linseed oilmeal, wheat middlings, 

 tankage, and skim milk; also one ration was composed of rice 

 polish and wheat bran. The pigs grew normally, and stored 



