Hygiene, although especially concerned with the maintenance of health, by a liberal interpretation may be made to include the means of prevention of certain diseases. It is, however, considered to be more convenient to apply the word " prophylaxis" to the science of prevention, although it is impossible to escape the conviction that every care that is taken to keep an animal in a healthy state necessarily includes the adoption of precautions to prevent the inroads of disease, whether common or specific.

Starting with the presumption that the science of Hygiene is to be applied to animals in a healthy condition and with the object of preserving health - in other words, prolonging the animal's life and keeping it in the highest state of efficiency for the work it is called upon to perform, - the question arises: What are the ordinary means by the agency of which this desirable end may be secured? The first thing which suseests itself relates to the function of nutrition. Even in a state of perfect animal idleness the ordinary physiological processes continue; oxidation, that is to say destruction, of tissues is always going on. Every movement of the animal, whether voluntary or involuntary, causes an appreciable amount of tissue waste; the waste products have to be excreted, as many of them are of a poisonous character, and the waste has to be replaced by new material. This repair of tissue demands a regular supply of solid and liquid food, containing the necessary materials for purposes of nutrition. Pure food and pure water in appropriate quantities are among the first essentials for the maintenance of life and health.

Closely connected with food and water, both being free from impurities as far as possible, is the air which the animal breathes. Even for the life of the most simple organisms air is necessary, and in the case of the higher organisms its withdrawal would be immediately fatal. And even when supplied in sufficient quantity it is capable of carrying with it deleterious constituents, some of them quite inappreciable by the senses under ordinary circumstances, but deadly in their influences to the animal's vital functions. The supply of a sufficient quantity of pure air at a proper temperature, and at the same time the elimination of stagnant air, is absolutely essential to the maintenance of health. Because, just as the process of nutrition implies the deposit of new material in place of the worn-out structures, which, if they had been allowed to accumulate in the system, would have poisoned the animal; so, on the other hand, the function of respiration is associated with the introduction into the system of fresh vitalizing air, and excretion of effete materials in a gaseous form, which, mixed with the air in the lungs, are exhaled at every expiration and discharged into the external atmosphere. These products of the respiratory process are poisonous, and if, owing to the absence of any means of escape from the building in which an animal is kept, they were permitted to accumulate, they would soon render the air contained therein effete and incapable of maintaining life and health. So it appears that food, water, and air, in proper quantity, and, so far as possible, in a state of purity, are the three primary conditions for the healthy environment.

It must be evident that the conditions above referred to are essentially concerned with the functions of organic life, and for the purpose of keeping a horse in the state of usefulness it may be further necessary that certain special organs should receive particular attention. The animal is required for purposes of locomotion. It is, therefore, indispensable that the feet should be kept in perfect condition; in other words, they cannot be left, as other parts of the organism may, to be maintained in a normal state under the influence of the ordinary reparative processes, because in domestication they are subjected to an excessive degree of wear and tear, from which in a state of nature they would be exempt.

The feet are protected by a covering of dense, but elastic, horny substance, which grows in proportion to the amount of wear which takes place under natural conditions, when the animal's movements are under its own control. In domestication, however, the experiment, which has been repeatedly tried, of working horses without some additional protection to the hoof has invariably failed, and the early practice of protecting the soles of the feet, or some portion of them, with iron plates or rings, is still continued with certain modifications, or, as they may be called, improvements. Still, the admitted value of the artificial protection is vitiated by the necessity for the use of nails as the means of fastening. The feet of the horse are, therefore, placed at a disadvantage in comparison with the rest of the organism, in consequence of the unavoidable application of artificial protection in the form of shoes which are attached to them by nails driven through a considerable portion of the hoof.

Added to the necessarily injurious consequences of shoeing are those which arise from the hardness of the roads; and the two adverse conditions will account for the failure, to a greater or lesser extent, of the feet during some period of the horse's life, in spite of all the care exerted for their preservation.

Under exceptional circumstances it has not unnaturally been considered that the feet require exceptional treatment, and numerous devices in the form of "stoppings" and hoof-dressings have been employed at various times for the purpose, it is alleged, of keeping the feet in a healthy condition. Of most of these appliances it may be said that the feet may be very much better without them. Moisture is very necessary for the maintenance of a healthy condition of the horn, and this is naturally absorbed by the horn tubes, of which the hoof is composed, when they are kept in a natural condition. But if the tubes are blocked by sticky or greasy substances, they cease to be able to absorb the moisture on which their elasticity depends. The hygienics of the foot demands that the organ should be left, as far as may be, in a natural state; the evils which are attendant on the application of shoes are in some measure unavoidable, and under the present improved state of the farrier's art they are reduced to a minimum. For the rest, it can only be said that the less the horny covering of the foot is interfered with the better.

Next to the feet the legs, or, as they are termed, lower extremities, as far as the knees and hocks, deserve consideration. These parts are exposed more than other parts to contact with irritating grit and dust and mud in the ordinary course of travel. Cracked or chapped heels or "grease" and other eruptive diseases are the consequences of this exposure, and some animals are susceptible in a high degree to influences which would leave other less-susceptible subjects untouched.

The skin over the whole of the body requires special attention in the horse to keep it in a healthy state, and the difference between a sensitive and insensitive skin has to be recognized in relation to a horse as much as in the case of the human subject.

Peculiarities of temperament have also to be taken into account as predisposing causes of disease of the nervous system, the digestive organs, and, in fact, the organs of the body as a whole.

Some kinds of food, again, tend to induce disorders of the integuments, and others to disturb the kidneys.

To detect and remove the various and often unsuspected causes which act in upsetting the balance of health in various ways is a task which necessitates close observation, and generally an amount of energy which is exhibited constantly by sanitarians in regard to the public health', but is rarely exerted for the benefit of the lower animals.