26th. Vegetable parasites. Trichophyton, achorion, microsporon, actinomyces, etc. (See parasites).
27th. Animal parasites. Lice, fleas, diptera, trombidium, Acari, ixodes, cimex, filaria, coccidia, etc. (See parasites).
GENERAL CAUSES OF SKIN DISEASES.
External. Internal. Traumas, abrasions, excoriations, lacerations, contusions, compression, radiating heat, scalding, incandescent objects, solar heat, chemical caustics, cold, freezing, kicks, bites, tusk horn or claw wounds, stings, venoms, envenomed bites, road dust, sweat, excretions, sebum, mineral and vegetable poisons, essential oils, fungi. Hyperæmia, exudation, depilation, sudation, moulting, climatic changes, unwholesome or irritating foods, ptomaines, alimentary fermentations, hepatic, renal or blood disorders, altered innervation, youth, age, temperament, heredity. Experimental nervous cases.
These may be external or internal or both.
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: