Before these different constituents of the plant can be used as food for animals, they must be prepared for absorption into the system of the animal. This preparation takes place in the mouth, œsophagus tube, the stomach, and the intestines, aided by the various secretions incident to digestion and absorption. Any withholding of any essential constituent has its result in inefficiency or illness of the animal. Withhold ash materials, for instance, from the food, or supply an insufficient quantity, and the fact will be evidenced by poor teeth, deficient bone construction and poor health in general. Let the feeding ration be short in protein, and the result will be shown in the flesh and blood. Let the carbohydrates and fat be withheld or supplied insufficiently, and energy will be denied and a thrifty condition will not be possible. The supply of these different constituents in the proper proportion gives rise to the balanced ration; and is concerned in a treatise of this kind only in so far as it has to do with disease or health. For, remember this fact: live stock are closely associated with right feeding. If foods be improperly prepared, or improperly supplied, or the rations poorly balanced, with too much of one constituent and too little of another, the effect will be manifest in an impoverished condition of the system. That means either disease, or disease invited. Not only must these facts be considered, but other matters given recognition also. The greater part of the trouble of the stockman in the way of animal diseases is due to some disturbance of the digestive system, or to the water supply, or to ventilation, or to the use to which the animal is put from day to day. Attention to the details of digestion has its reward in thrifty, healthy stock; a lack of this attention brings trouble and either a temporary ailment or a permanent disease. =Process of Mastication.=--Food is taken in the mouth, where it is masticated by means of the teeth, lips, cheeks, and the tongue. While the process of mastication is taking place there is being poured into the mouth large quantities of saliva, which softens the food and starts the process of digestion. The active principle of saliva is a soluble ferment, called ptyalin, that converts the starch of food into sugar. The amount of saliva that is poured into the food is very great, being often as much as one-tenth of the weight of the animal. This ferment is active after the teeth have been formed, which explains why it is not advisable to feed much starchy food to children before their teeth have begun development.