434 FORBES: MINERAL ELEMENTS IN NUTRITION 



Now we have shown that the mineral nutrients of bluegrass 

 vary more than 100 per cent in accord with the fertility of the 

 soil. The skeletons of growing animals respond readily to the 

 mineral nutrients of the food. There is no definite upper limit 

 of phosphate deposit in the bones. The quality of the grass 

 must affect the quality of the bones; and strength and sound- 

 ness of bone favor long-sustained efficiency. Probably the 

 greatest strain to which the bones of animals are subjected is 

 in the service of our large, early-maturing horses on hard-sur- 

 faced roads and pavements. The most famous horse-breed- 

 ing center of the United States is a region of limestone soils and 

 luxuriant bluegrass which our analyses show to be unusually 

 rich in bone food. We have always bowed while the Kentuckian 

 asserts that his state produces the most beautiful women and 

 the finest horses in the world, and now we know that in so far 

 as these claims depend upon a superior quality of bluegrass 

 they rest on a substantial basis of fact.- 



It is also true that in many localities in this country, on im- 

 poverished soils, we find horses and cattle suffering from mal- 

 nutrition of the bones. This ailment is most common during 

 periods of rapid growth or milk production, especially during 

 and immediately after seasons of drouth and restricted food 

 supply. This condition responds readily to treatment with 

 calcium phosphate. 



Among the several mineral elements present in foods in minute 

 quantities especial interest attaches to iodine, because of its 

 importance in metabolism. The only tissue in the bodies of 

 vertebrate animals which contains iodine in apparently essen- 

 tial relations is the thyroid gland. The iodine content of the 

 thyroid may be increased by the administration of iodine; one 

 of the active principles of the thyroid is its iodine-containing 

 constituent; and goiter in certain stages responds favorably to 

 iodine treatment. Further, there is a marked and continuous 

 local prevalence of goiter in many regions. These facts furnish 

 sufficient basis for our interest in the iodine content of foods. 



In our study iodine was estimated in 927 samples of animal 

 and vegetable products. These products were in part common 



