We may define hunger as appetite (p. 104) in excess.

Thirst is the desire to drink, caused by functional necessity, and accumulation, in the body, of decomposition products which require water for their removal. Colin tells us that if a horse is thirsty while he is eating, he will chew his food slowly and the flow of saliva will be languid. He will soon stop feeding, will become restless, will look about him, and will often neigh for water. If he is outside, he will make strenuous efforts to get water. We all know how a thirsty horse plunges his muzzle into water, and how he will try to resist any attempt made by his ignorant or cruel master or groom to prevent him from satisfying his longing for that fluid. If his thirst continues to remain unappeased, his uneasiness will increase, his mouth will become dry from want of saliva, his tongue hot, his blood thick, fever will set in, digestion will become checked, and constipation will ensue from the dry and balled condition of the food in the intestines. We may take for granted that severe thirst is a very painful feeling in horses, and that it can cause much more distress than hunger.

When a horse suffers from hunger alone, or from hunger and thirst, he at first becomes excited and ravenous; but later on, he becomes affected with increasing depression, which soon deprives him of all desire for food, even if it is offered to him; and his temperature becomes lower and lower. The torpor appears to be largely due to the great increase, in his system, of poisonous products, caused by the breaking up of nitrogenous tissue, after the other sources of heat production have become more or less exhausted. The fall in temperature naturally results from the small supply of energy available in the body.

Death seems to be produced principally by an insufficient supply of energy; by disintegration of the tissues; and by poisonous effects of an excess of nitrogenous waste. Towards the end, the horse remains lying on his side, and death is preceded by cold sweats and a few brief convulsions (Colin).

A bility to bear abstinence from food depends mostly on age; percentage of fat in the system; and general health. As the needs of the system are more pressing, and the process of waste is more active in young horses than in mature ones; they are of course less able to endure privation of food and water. The advantage of age naturally decreases as the animal's health becomes enfeebled with the weight of years. Colin states that when horses are deprived of all food except water, thin ones will live on an average only from five to ten days; and fat ones, from three to five weeks. Twelve or thirteen days appear to be the maximum length of time which a horse can live, when he is deprived of both food and water.

We have seen (p. 94) that sugar dissolved in water is the best means for resuscitating a horse which is dying from hunger. In making this attempt, or in trying to save a horse which is dying from thirst, the food or drink should be given in small quantities at a time, and at intervals appropriate to the enfeebled condition of the animal's digestive organs. The same principles, including the use of sugar, should be carried out with human beings placed in similar circumstances.