MAINTENANCE OF FARM ANIMALS 65 



globin, an iron-protein compound in the red corpuscles. In the stomach 

 the pepsin acts only in the presence of an acid, normally hydrochloric, 

 derived from the salts of this acid present in the blood. 



96. Mineral compounds control life processes. In some mysterious man- 

 ner, possibly by carrying electric charges which stimulate the body 

 cells, 11 the mineral compounds of the body direct its various vital proc- 

 esses. A simple experiment often performed in the laboratory will 

 illustrate the important functions of the mineral elements in life. If 

 the heart, still beating, is removed from a frog and placed in a solution 

 of pure sodium chlorid (common salt), its beats soon fade out. Now if a 

 small amount of a calcium salt (lime) be added to the solution, the heart 

 will at once begin to beat again, and will continue in rhythmical con- 

 traction for some time. Unless a small amount of a potassium salt 

 is also added, the beat will not, however, be normal, but the heart 

 will fail to relax quickly and completely enough after each contraction. 

 Therefore, if potassium is not added the relaxations become more and 

 more feeble, until the heart stops in a contracted state. Not only 

 must potassium be present, but there must be a correct proportion be- 

 tween the amounts of calcium and potassium. If too much potassium 

 is added, the heart will fail to contract properly, and finally will again 

 stop beating, but this time in a state of complete relaxation. 



Similarly, the other vital processes are dependent not only on the 

 presence of various mineral salts, but also on a proper relationship 

 between them. Therefore it will be seen that unless the amount of 

 these mineral salts in the blood is kept normal, serious consequences 

 will follow. In large measure the kidneys protect the animal against 

 an unbalanced mineral matter content in the blood by promptly ex- 

 creting any excess of various salts which may be present. However, 

 when the food continually furnishes the blood an unbalanced salt 

 mixture, the kidneys may be unable to keep the blood composition 

 normal, with resultant injury to the animal, For instance, magnesium 

 and calcium seem antagonistic in their action, and in voiding the 

 excess of magnesium the body loses calcium. Given in excessive 

 amount for long periods, feeds which contain much magnesium in 

 proportion to calcium, such as wheat bran and middlings, are said to 

 cause a weakening of the bones, leading to such troubles as "bran 

 disease" or "miller's horse rickets." 



Appendix Table VII sets forth the mineral constituents of representa- 

 tive feeding stuffs. 



97. Mineral requirements for maintenance. The common feeding stuffs 

 contain all the necessary mineral salts, at least in small amounts. As 

 a rule, the roughages, except some of the straws, are much richer than 

 the grains in mineral matter. Moreover, the body is probably able to 

 use many of the mineral compounds over and over, taking them back 

 again into the circulation after having been used. Therefore, for 



"Forbes, Ohio Tech. Bui. 5. 



