444 FORBES: MINERAL ELEMENTS IN NUTRITION 



Throughout these studies of the influence of foods upon the 

 nutrition of swine numerous effects of the mineral constituents 

 of the rations on minor details of qualitative composition of 

 the tissues have been noted, but the importance of such effects, 

 as related to the functions of the parts, has not been demon- 

 strated. 



Our latest study in mineral metabolism was with cows. The 

 milch cow greatly excels any of the other farm quadrupeds in 

 the rapidity and efficiency with which she produces proteid and 

 mineral nutriment. This unrivaled productive capacity calls 

 for as unusual supplies of the kinds of nutriment involved. 

 So far as protein is concerned this requirement is amply recog- 

 nized; but, with almost no evidence on the subject, we have 

 assumed that the cow's mineral requirements are fully met with- 

 out any attention being given to the matter. Our results show 

 this assumption to be unwarranted and untrue. 



Six cows were used in this study, in two groups of three each. 

 Each cow was taken through three experimental periods, usually 

 of 19 or 20 days' duration, separated by 10-day intervals. The 

 excreta were caught by attendants sitting behind the cows. 

 Complete ash analyses, as well as ordinary proximate analyses, 

 were made on foods, milk, urine, and feces. 



We found that liberal milk production, on common practical 

 winter rations fed in quantities sufficient to maintain the live- 

 weight and to cause regular and extensive nitrogen and sulphur 

 storage, caused large and consistent losses of calcium, magnesium, 

 and phosphorus from the skeleton. These losses occurred in 

 spite of liberal supplies of these nutrients in the food. The very 

 limited response of the cows to large increase in the intake of 

 these elements suggests that the selective improvement of the 

 milch cow, for milk production, has outrun her capacity to digest 

 mineral nutrients. A further study is in progress in which we 

 hope to learn whether under any circumstances it is possible 

 to protect the cow from loss of minerals during heavy milk 

 production. 



An extensive metabolism of silicon was demonstrated ; and an 

 excess of inorganic acids over inorganic bases in the ration, due 



