At the head of the list stands opium, where Percival, the father of veterinary medicine, placed it, and described it as "the sheet anchor of the veterinarian". Its method of production need not be described here.
Fig. 432. - Opium Poppy (Paparer somniiferum).
1, Capsule showing Turkish method of incision to get opium. 2, Seed. 3, Section of seed.
Opium as imported is a blackish-brown, pasty-looking substance. The chemist is able to separate from it some nineteen or twenty alkaloids, of which the chief are morphia and codeia. The preparations used in veterinary practice are the gum, the powder, tincture (laudanum), morphia, and occasionally codeia.
When an aqueous preparation is required the extract is rubbed down with hot water. The compound tincture (paregoric elixir) is also sometimes prescribed.
The chief method of administering morphia is by subcutaneous injection. This course is adopted as a matter of convenience, and not, as in the human subject, to avoid those derangements of the stomach and bowels which so commonly follow its use when given by the mouth.
Externally the tincture and extract of opium are used to allay pain, and it is generally believed that greater anodyne effects are produced upon an abraded surface than when applied to an unbroken skin. In inflammatory oedema, and sprains to tendons, joints, and contusions, its application in conjunction with acetate of lead and spirit of wine has long been resorted to on account of its soothing and sedative properties.
Internally administered, opium affects horses in different ways and in proportion to the dose. In small doses it is a stimulant. Long continued it becomes astringent and induces constipation, although a medium dose be employed. Its effect in controlling pain and spasm of the intestine has been recognized for ages. It is also employed in diarrhoea and other diseases in which purging is a prominent symptom.
Large doses are sometimes given to restive horses that will not submit to operation, and that for special reasons cannot be submitted to other forms of restraint; and in a few instances only is the same degree of excitement observed to follow its use, as marks its immediate effects on man.
Belladonna, and Atropia, its active principle, belong to the same class of anodyne and sedative drugs as opium, and may be alternated with or used in conjunction with it. Besides allaying pain and spasm when externally applied or internally administered, it would seem to be specially beneficial in its action upon the organs of vision and upon the urinary and generative apparatus. The pupil of the eye is dilated, either by internal doses or the more convenient method of dropping a solution of atropia on the surface of that organ. In some diseases in which the iris is liable to become fixed to adjacent parts under conditions of inflammation, this is prevented by causing the pupil to be dilated and removing the iris from contact with the structures referred to.
Fig. 433. - Belladonna (Atvopa Belladonna).
1, Corolla opened. 2, Pistil. 3, Fruit. 4, Section of fruit.
Opium has the contrary effect, and causes the pupil to contract.
In irritability of the bladder and kidneys belladonna is found to be a valuable drug, controlling pain and inducing normal secretion, while its properties render it of great value when injected into the uterus of mares after painful labour or inflammatory action from eversion or other accident.
Atropia, its active principle, is invariably employed in solution, either as drops for the eyes or for subcutaneous injection.
Hyoscyamus or Henbane is a drug of like therapeutic effect to belladonna, but not in general repute among veterinarians. It may, however, be employed with advantage in the few cases where some idiosyncrasy brings disappointment to the prescriber who has given belladonna. Its action is invariably milder and the results apparently better when given in combination with some other sedative.