Parasites are minute animals which infest and feed upon other animals; and parasitic diseases are the disorders which these intruders set up.

Parasites may be arranged into two classes, - Epizoa, or external; and Entozoa, or internal.

The parasites of this class are divisible into: (1.) Those that live on the surface of the skin; and, (2.) Those that live in its proper structure.

1. Parasites Living On The Skin

(a) The louse, resembling, but larger than, that of man, and unable to live on the' skin of the human being.

(b) The flea.

(c) The tick, varying in size, sticking firmly to the skin by claws, producing great local irritation, and appropriating to itself a large quantity of the dog's blood by suction.

Symptoms

Lice excite considerable irritation and itching of the skin, followed, when present in large numbers and in a chronic case, by a peculiar papular eruption - Prurigo pedicularis. The itching causes the dog to rub and scratch himself, with more or less vigour; red streaks, dotted with minute drops of congealed blood, may then be seen on the skin. The tops of the small pimples may be rubbed off, and a little serum exuded; matter may even form on them if the general health be bad. Lice, besides being the direct cause of these eruptions, and by inducing scratching, may also invade a skin previously diseased.

Dogs in bad health, living on poor food, and breathing foul air, are peculiarly liable to be infested with these vermin.

Treatment

The parasites must be killed, and that without injuring the dog. Soft soap and warm water should be thoroughly rubbed, not merely on the hair, but into the skin, so as effectually to reach the roots of the hair, until a good lather is produced. The dog should then be thoroughly drenched with, or dipped into, tepid water. When thoroughly cleansed by these means, the skin and hair should be dried before a fire, and by friction with a towel. In bad, or obstinate cases, it is a good plan to thin the hair, in order that the lice may be the better reached. After drying, the nits, which adhere to the hair, should be removed by sprinkling the surface with tincture of camphor, and afterwards carefully combing and brushing. The lips and eyelids, where such creatures most congregate, must not be forgotten. It may be necessary to repeat these processes once or twice. A dose of Arsenicum should be given three times a-day to cure the eruption, which, however, generally disappears of itself when its lively cause is removed.

The old bedding should be destroyed; in fact, the dog should sleep in a new place ever after the first dressing; or until, by fumigation, washing, painting, etc., the parasites and their nits are effectually destroyed. Shavings, or hay, are the best materials for bedding.

In some cases, instead of camphor, Staphysagria may be used, either sprinkled on in the form of powder, or rubbed in as the decoction. Merc. cor.* also destroys the parasites; but care should be taken lest salivation take place. The latter is the best application for ticks.