Part 83

=External Causes.= Some affections of the skin are due to external causes exclusively, while in others the local cause of irritation is accessory but no less important in maintaining the trouble. Among the more prominent external factors may be named: traumatisms, abrasions, excoriations, lacerations, contusions, compression, radiating heat, boiling water, hot or incandescent solids or liquids, solar heat, chemical caustics and irritants, cold, freezing, injuries by harness, kicks, lacerations with teeth, tusks, horns or claws, stings, bites, (leeches, snakes, etc.), venoms, (snake, toad, etc.), road dust and sweat, liquid fæces or urine, excess of sebum in sheath or vulva, mineral poisons (mercurial, iodides, bromides, arseniates, caustic alkalies, caustic salts, etc.), vegetable poisons (croton, bryonia alba and dioica, heracleum or cow parsnip, polygala or milk wort, cyclamen or sow bread, polygonum hydropiper, mustard, œnanthe, cicuta, hypericum perforatum and androsaemum, rhus toxicodendron, radicans and venenata, capsicum, pepper, radish, Indian syringa, anemone nemorosa and patens, ranunculus acris, scelerata, flammula, mericatus and bulbosus, cytisus, euphorbium and the essential oils of turpentine, origanum, lavender, etc.), fungi of musty food, ergot, etc.

=Internal Causes.= Among these are all conditions that induce stasis in the capillaries or lymph vessels, active hyperæmia, exudation, depilation, profuse perspiration, shedding the coat, exposure to cold, chill, etc., sudden access of warm weather, poor and insufficient or rich, stimulating food, cotton seed meal, indian corn, buckwheat, purple clover, animal food (in dogs), spiced food, food spoilt by wet and cryptogams, indigestions, gastric and intestinal fermentations, hepatic disorders, renal disorders with imperfect elimination, blood disorders, and nervous disorders which entail vaso-motor changes. Early age predisposes to some affections (variola, warts); old age to others (eczema). A nervous temperament in horses favors the drier eruptions (pityriasis), a lymphatic temperament the exudative (grease, canker, moist eczema). A hot, moist season favors most skin affections (eczema, acariasis, etc.), dry insolation others (erythema) and cold still others (chillblains, frost bite, chaps, etc.). Some eruptions are at first summer troubles, disappearing on the advent of cold weather, yet in time the predisposition increases, or the inflamed skin becomes less resistant and the disease becomes permanent. A marked predisposition in certain animals, appears to inhere in the constitution and proves hereditary in the family (Blain, Lafosse, Cadeac). Nervous causes have not been satisfactorily traced in the lower animals, yet the dermatitis of the face and neck caused by the experimental lesion of the cervical sympathetic or its connecting ganglia shows clearly enough how any portion must be affected by disorder of its trophic or vaso-motor nerves. Charcot found that experimental lesions causing inflammation of the spinal cord, led to trophic changes and finally gangrene of a corresponding part of the skin. Babesiu and Israï injected oil of mustard in one side of the cord, in three dogs, and found in several days a vesicular eruption and atrophy of the skin on the same side, a result they supposed of the myelitis.

DIAGNOSIS OF SKIN DISEASES.

Diagnosis. Clip or shave skin. Examine in warmth: skin and mucosæ, where uninjured by rubbing, moisture, dryness, color, odor, discharge. Soapy wash. Exudation into skin: pliancy: rigidity: eruption: tenderness, itching, history, association, feeding, watering, exposure, housing, harnessing, driving. Coincident disease. Prognosis. Microbian dermatosis, parasitic dermatosis, external irritants, ingested irritants, toxic systemic products, constitution, renal disease, movement of joints, harness.

The thick hairy covering of animals, and the vicious energy with which they often rub, scratch and bite themselves, thus turning simple into extensive and severe lesions, interfere seriously with a satisfactory diagnosis. The following precautions are usually demanded:

1st. Clip the animal close to the skin to allow of careful examination. In some affections, this may be dispensed with, but as a rule it should be followed. What appears to be a circumscribed eruption may be shown to be general, or at least extensively diffused over different regions. Or what was shown only by scurf or scab may be seen in its earlier and more characteristic stage as erythema, papule or vesicle. It may even be desirable to shave the affected part, care being taken, not to slice off the characteristic papules, etc.

2d. Make the examination in a clear day in full sunshine if possible. In dark, cloudy weather, and in dimly lighted stables it is impossible to identify the different lesions. Artificial light is very unsatisfactory. Warmth, as in sunshine, or in a warm day or room, increases any itching and the cutaneous circulation and congestion, and renders more lively and active the animal parasites that may be present. These may be found in the surface scrapings taken in warmth, and not at all if taken in cold. A hand lens will assist in the discovery of the larger parasites, while for the smaller ones the microscope must be employed.

3d. Examine carefully all parts of the skin and even the visible mucosæ, estimating whether any lesions of the latter indicate extension from the skin, by proximity, or a general constitutional affection. Scrutinize particularly such parts as have not been abraded by mechanical injury—those which show the primary character of the lesion. Is the affected portion of the skin dry or moist? Some eruptions like impetigo or grease are always moist, others like pityriasis or dry eczema are habitually dry apart from mechanical injuries. Ascertain the color, odor and consistency of any discharge. It may be a limpid or reddish serum in grease, honey like in impetigo, oily in farcy, greasy in swine plague. The odor is fœtid in grease, canker and thrush of the frog, cheesy in variola, and mousy in favus.

4th. To learn the true nature of the eruption a warm, soapy wash may be essential to remove scurf, scab, and other encrustations.

5th. Note the depth and extent of the skin lesions, the thickening of the skin, its pliancy or rigidity, its adhesions to subjacent parts or free movement upon them, whether it is contracted into folds or ridges, the degree of congestion, the nature of the eruption, uniform congestive redness, papule, vesicle, pustule, squama, sore, ulcer, nodule, slough, etc. Are the individual lesions isolated or confluent?

6th. The presence of itching and its degree are important data. Pruritus is always excessive in ordinary acariasis, marked in eczema, phthiriasis, and some neuroses, and very slight in a number of skin affections (pityriasis, ringworm, grease, thrush, contagious acne). The abrasions and sores caused by rubbing, scratching, etc., will usually give a key to the degree of pruritus, and handling the part will render the condition evident.

7th. The history of the case is always important. Is it chronic or acute? Continuous or intermittent? Associated with any special conditions of proximity to other diseased animals, to special feeding, watering, exposure, housing, harnessing, driving, which might account for it? Did there coincide with its eruption any indigestion, gastric or intestinal, or any hepatic, urinary or nervous disorder on which it might be dependent?

Prognosis. This is subordinate to the nature, causes, course, duration and complications of the disease.

=Microbian dermatosis= (variola, aphthous fever, rouget) usually follows a rapid course and recovery is perfect with some measure of immunity.

=Parasitic dermatosis= (acariasis, phthiriasis) is liable to have serious secondary results (infection to man or animals, loss of wool, tender skin), and to run a chronic course.

=Maladies from external irritants= (chafing, caustics, traumas, vegetable, or animal irritants), do not tend to chronicity and are often promptly curable.

=Maladies due to ingested irritants= (urticaria, distillery waste eruptions), also tend to recovery when the source of irritation is cut off.

=Maladies due to toxic products of the system= will be obstinate or incurable, in ratio with the incurability of the causative factor. Those due to the absorbed products of a simple indigestion, will tend to terminate with the removal of the cause, while those dependent on chronic and perhaps irremediable disease of the digestive organs, liver, or kidneys will be correspondingly inveterate or incurable.

=Maladies due to a constitutional vice=, in sanguification, nutrition, innervation, etc., are likely to be irremovable or only temporarily curable.

=Burns and some other skin diseases= are liable to become complicated by renal embolisms, albuminuria, indigestions, etc., which may render the skin affection inveterate or incurable.

=Dermatitis= on the folds of articulations or on the seats of harness, are sustained by the local irritation, and may necessitate long rest, or abstention from work requiring the use of such harness.

All dermatites are liable to show special features of inveteracy, or amenability to treatment according to surrounding conditions—hygienic or otherwise.

GENERAL PRINCIPLES OF TREATMENT OF SKIN DISEASES.

General and local. Diet: wholesome diet following laxative: restricted, generous, vegetable. Rest, avoiding congestion, perspiration, friction, stretching, pressure. Cleanliness. Diuretics. Purgatives. Tonics. Alteratives. Sulphur. Antimony. Phosphorus. Calcium sulphide. Pilocarpin. Baths, tepid, warm, soapy, alterative. Emollients, simple, medicated. Drying powders. Protective films. Stimulating and antiseptic applications. Parasiticides. Caustics. Counter-irritants. Bandages.

These must be general and local, and the first hygienic, dietetic and medicinal.

The =diet= is especially important in eruptions due to poisons such as green food, distillery refuse, silage, roots, ergoted or smutty food, musty fodder, irritant plants in hay or grain feed, buckwheat, etc. In many cases a change to sound fodder and a laxative to clear the alimentary canal of the irritant, may be all that is required. In cases where the feeding has been parsimonious, a judiciously gradual change to a generous diet may be required. Again when the feed has been unduly rich, or spiced as in the patent food for stock or the table leavings for dogs, a plainer, simpler and less exciting diet will be called for. Indigestions, urinary and hepatic disorders due to diet may be often corrected by a more judicious ration.

=Rest= is a most important element in horses and hunting dogs. When pressure of the harness keeps up the irritation, or when active movement reopens cracks in the tense rigid congested skin of the heel, carpus or tarsus of the horse, the parts must be kept quiescent. When on the other hand chaps and fissures are caused and maintained by stocking, the patient may do much better with exercise. In skin congestions which are aggravated by work and increased cutaneous circulation, rest is imperative.

=Cleanliness= is no less imperative. Many cases are started and maintained by filth on the skin and in the air of the stable and hence sponging, currying, brushing, rubbing, are directly therapeutic. Yet care must be taken to avoid irritation where the skin is tender. In the sensitive heels of the horse congestion, chaps, and stocking are often determined by washing in ice cold water and leaving to dry uncovered, in a draught of air, or by washing with common laundry soap having alkali in excess. Even tar soap will sometimes keep up the trouble in a specially sensitive skin. Apart from such exceptional conditions, thorough grooming is commendable, not only in cleaning the skin, but in improving its circulation and nutrition.