FUNCTIONS OF THE NUTRIENTS 157 



duction successfully through two periods of lactation are 

 due to the removal from the body of these mineral elements 

 not supplied in sufficient abundance in food. It would 

 seem, however, that ordinarily there are periods during 

 which a milch cow recovers her loss of mineral elements. 



Forbes calls attention to the importance of iodine in 

 animal metabolism. It has long been known that in the 

 cases of abnormal physical development accompanied 

 by inferior intellectual quality, such subjects being known 

 as cretins, the physical and mental conditions have been 

 improved by an extract of the thyroid gland which car- 

 ries iodine. An extensive investigation of many feeding- 

 stuffs shows an absence of iodine in some and only traces 

 or very small percentages in others. It would appear, 

 however, that under the ordinary system of feeding mixed 

 rations the iodine supplied to our domestic animals 

 is sufficient. 



228. Relative efficiency of different phosphorus com- 

 pounds. The mineral elements of foods may be supplied 

 to the animal in various forms. This is particularly true 

 of phosphorus which is used so freely by growing animals 

 and milch cows. Because of the importance of this ele- 

 ment the problem of the relative nutritive efficiency of 

 organic as compared with inorganic phosphorus com- 

 pounds has been much studied. The organic forms found 

 in foods are in part nucleo-proteins, phospho-proteins, 

 phytin, and similar compounds found in grains, and 

 lecithin and glycero-phosphates. In an admirable re*sume* 

 of the whole subject, Forbes shows that the data secured 

 on this question give conflicting testimony but that the 

 majority of evidence seems to favor the conclusion that 

 the organic phosphorus compounds are more efficient, 

 for some species at least, than the inorganic, such as cal- 



