ARID AGRICULTURE. 



315 



WHAT FOODS 

 CONTAIN 



MINERAL 



profitable flow of milk. Young animals need the 

 growth-forming nitrogen compounds. Older 

 animals need more starch and fat. Following 

 out these principles in even a rough, general way, 

 always results in more profitable feeding. The 

 key to scientific feeding is the balanced ration, 

 and the more nearly balanced it can be made the 

 better the results. Good rations may be made 

 up of different combinations of feeds and one 

 combination may be much cheaper than another. 

 If in balance, the cheaper feed will give as good 

 results to the animal as one that may be much 

 more expensive. 



Animal foods are essentially organic, i. e., 

 they are complex substances which have been 

 built up and compounded by some form of plant 

 life or are taken from animals which have ob- 

 tained them through plants. Animals cannot 

 live on mineral matter alone, but some of the 

 salts, found in the ash, when organic substances 

 are burned, are essential to them. Sometimes 

 they need more salt than they obtain from their 

 natural food and it pays to supply common salt 

 to all farm animals, or wood ashes and coal dust 

 to fattening pigs. While the composition of or- 

 ganic substances is very complex, the food com- 

 pounds may be grouped in the following four 

 classes: 



While mineral salts are necessary to supply 

 the inorganic substances found in the bones and 



