MAINTAINING FARM ANIMALS 55 



protein, carbohydrates, and fat, the animals will die thru mineral 

 starvation, and generally the end will come more quickly than if no 

 food at all is given. Mineral matter is found in all the vital parts of 

 the body. The life centers of all the cells are rich in phosphorus 

 and the skeleton is largely composed of calcium (lime) combined with 

 phosphorus. As we have seen, the power of the blood to carry oxygen 

 is due to hemoglobin, an iron-protein compound in the red blood 

 corpuscles. In the stomach, the pepsin acts only in the presence of 

 hydrochloric acid, a mineral compound derived from mineral salts 

 in the blood. 



A simple experiment often performed in the laboratory will illus- 

 trate the manner in which mineral salts control life processes. 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 rhyth- 

 mical contraction for several hours. Unless a small amount of a potas- 

 sium salt is likewise added, the beat will not, however, be normal, the 

 heart failing to relax quickly and .completely enough after each con- 

 traction. The relaxations will 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 between 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. 



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 com- 

 pounds over and over again, taking them back again into the circula- 

 tion after having been used. Therefore, for animals which have 

 finished their growth, the usual rations containing roughage furnish 

 sufficient mineral matter, except common salt. As shown later, it is 

 advisable to supply farm animals common salt in addition to that in 

 their feed. Since large amounts of calcium (lime) and phosphorus 

 are needed to build the skeleton, these elements may fall short in 

 rations for young animals. 



Calcium and phosphorus. — Over 90 per ct. of the mineral matter 

 in the skeleton consists of calcium and phosphorus. "When the supply 

 of either of these is low in the feed, the skeleton acts as a storehouse, 

 doling out these mineral elements so that the life processes of the body 

 may continue normally for a time. But such withdrawal of mineral 

 matter from the bones makes them porous and brittle. Indeed, in 



