THE PROCESS OF DIGESTION 79 



intestine, and goes through no special digestive changes as 

 with the other food substances. Mineral substances, such 

 as lime and phosphorus, are regarded as of great importance 

 in building up the body. Those foods that contain but little 

 ash give poor results in feeding, unless the necessary mineral 

 material is supplied. Years ago Professor W. A. Henry 

 showed that hogs fed only corn had bone just about half as 

 strong as hogs fed bone meal or hard- wood, ashes with the 

 corn. Farmers give ashes or coal to hogs because these ani- 

 mals make a better development when so fed. Without the 

 ash, the body is not given proper nutrition. Corn lacks ash. 



Figure 21. The influence of minerals on the development of swine. The 

 pig on the left received a ration with sufficient minerals, the other was 

 given a ration deficient in minerals. Note the difference in bone and 

 growth. Photograph from Iowa Experiment Station. 



A hundred pounds of corn meal contains but a pound and 

 a half of ash, while a hundred pounds of oats has more than 

 twice that amount. All stockmen rate oats highly for pro- 

 ducing hard, strong bone in growing animals. The legumes, 

 such as clover and alfalfa, supply much needed mineral 

 material in the food of farm animals and so their use should 

 be generally advised, especially for cattle, sheep and swine. 

 All food has a heat value, just as coal has. If burned, 

 coal gives off heat; so does food. All heat comes from the 

 sun, and is stored up in the plant, ready to be set free. 

 The word calorie represents a measure of heat given off by 

 food. One calorie equals the amount of heat required to 



