334 NUTRITION OF FARM ANIMALS 



in the upper part of the intestine where the contents are acid, 

 while more or less of it is excreted again in the lower intestine. 

 While it is impossible, therefore, to determine by means of the 

 ordinary digestion experiment how much of such ingredients 

 have actually been resorbed and excreted again and what 

 proportion has escaped digestion, it appears safe to conclude 

 that at least a considerable share of them has been dissolved and 

 resorbed in the upper digestive tract and that the insufficiency 

 of certain rations as regards mineral ingredients is not due to 

 the indigestibility of the latter. 



424. Contrast between organic and inorganic nutrients. 

 There is an obvious distinction between organic and inorganic 

 nutrients. The former may be said to be destroyed in the 

 performance of their functions. A molecule of dextrose or of 

 stearin, for example, can yield energy to the body only by being 

 split up and oxidized step by step to carbon dioxid and water. 

 The case is similar with protein so far as it is used for fuel pur- 

 poses and even its specific functions seem to involve the cleavage 

 and oxidation of its molecules. With the electrolytes contained 

 in the body the case is different. A molecule of disodium 

 phosphate, for example (or its ions), is not destroyed by the 

 performance of its functions in maintaining neutrality no matter 

 how long it serves that purpose and the molecule of sodium 

 chlorid contributes its quota to the osmotic pressure of the 

 blood serum as long as it remains dissolved in that fluid. Only 

 as it escapes from the body will the need for a fresh supply 

 arise. 



Losses of ash 



425. Causes of loss. So far, therefore, as the maintenance 

 of mature animals is concerned, the magnitude of the ash re- 

 quirement will be substantially determined by the rate at 

 which the various elements are eliminated from the body 

 through the excretory organs. In growing animals there is in 

 addition, of course, the demand for ash ingredients for structural 

 purposes, both for the building up of the skeleton and to a less 

 degree of the soft tissues, but even in this case the total ash 

 requirement is determined in large degree by the rate of ex- 

 cretion. 



