Mercury is a liquid metal, and in various forms of chemical combination is largely employed in veterinary medicine in both internal and external disorders. The preparations used in the treatment of horses are calomel, bichloride or perchloride of mercury (corrosive sublimate), gray powder, blue pill, red and white precipitate, nitrate of mercury, iodide and bin iodide of mercury, yellow oxide of mercury, mercurial ointment, oleate of mercury, etc.
As an external remedy mercury is used for various skin diseases, particularly those caused by parasites, both animal and vegetable. The blue ointment, which is simply a mixture of mercury and lard, with a small proportion of suet to harden it, was formerly very much used, but at the present time has given place to the cleanlier preparations of ammoniated mercury, the red oxide, and the nitrate, while the red iodide or biniodide, as it is respectively called, is the material most used in blisters, and was originally introduced as a substitute for firing.
The bichloride or perchloride (the change of nomenclature gives rise to confusion, and we therefore use both terms) is an invaluable chemical for the destruction of external parasites, as well as those minute organisms which are now regarded as the cause of so many specific contagious diseases. Besides its medicinal use it is employed as an antiseptic for the sterilization of instruments, and the hands of the operator in the course of surgical operations. Calomel is the chief salt of mercury given to horses. It is not, however, in great favour. As a liver stimulant it is largely employed in human and canine medicine, but in the horse it is feared on account of its sometimes drastic effects. That it is valuable as an alterative is, however, a matter of common knowledge among those who have the care and conditioning of horses for fast work.
Though the action of mercury upon the system is obscure, it is nevertheless marked. It is absorbed from the blood by every tissue of the body, and to produce its constitutional effects it is frequently prescribed in the form of solution of the perchloride. It influences nutrition in some obscure way, and excites absorption of various morbid deposits. When given over a long period it tends to accumulate in the system, and to prejudicially influence the health of the animal, and can be found in the tissue's after death. Inflammatory deposits are caused to be absorbed by it, and it was one of the remedies used in the coaching days when glandered teams were kept at work by the use of such drugs and enabled to enjoy a certain measure of health.
Mercurial poisoning is generally spoken of as salivation, because the first prominent symptom is a profuse discharge of saliva from the mouth, accompanied by swollen and inflamed gums, a very offensive odour from the breath, pasty tongue, loss of appetite, etc. In our patient, the horse, it is seldom the result of intentional druoo-ino;. It has been known to occur, however, as the result of a horse licking itself or other animals when mercurial ointment has been lavishly employed for skin troubles. It may also result where animals have picked up mercurial pigments, and in the neighbourhood of quicksilver furnaces it sometimes appears from the consumption of herbage contaminated with fine particles of cinnabar - the mineral from which it is chiefly obtained. In advanced cases of mercurial poisoning, lassitude, wasting, and the passage of blood-stained faeces are among the more prominent symptoms. There is no specific antidote to mercury as a poison, but animals frequently recover from its effects when removed to a suitable environment, receiving plenty of fresh air and a liberal diet supplemented by milk, eggs, and linseed.