270 DISEASES OF THE SKIN 



(h) Squamate eczema, where the epidermis is covered with 

 masses of scales. 



(i) Seborrhoic eczema, where the crusts are infiltrated with 

 masses of fat from the sebaceous glands, forming white or 

 yellowish, greasy scales. 



(j) Sycosiform eczema, which is an inflammation of the 

 hair follicles, forming papules or pustules that are perforated 

 by hairs. 



Etiology. — The causes of eczema are usually external, and 

 consist in mechanical, chemical, thermic, and infectious irri- 

 tants. The most common of these is neglect of skin cleanli- 

 ness. Eczema, therefore, is most often seen on parts of the 

 skin of the horse where the least grooming is done. On the 

 other hand too much water coming in contact with the skin 

 can produce eczema. Examples are the eczema of sheep from 

 exposure to excessive rainfall, effect of dewy pastures, muddy 

 roadways, etc., upon the skin of the legs of horses or the too 

 frequent bathing of dogs. Eczema can also originate from 

 the discharge in diarrhea, incontinence of urine, and profuse 

 sweating. The mechanical insults which produce eczema are 

 insect bites (fleas, lice), biting, rubbing, and scratching on the 

 part of the patient and. the friction of the harness or saddle. 

 Thermic influences are cold, the sun's rays (solar eczema), 

 or fire. Many chemicals can produce eczema, such as mer- 

 cury, mustard, tobacco, etc., when applied to the skin. Mer- 

 cury or iodin given internally for a long period of time can 

 have the same efl^ect. 



Internally eczema, or more properly exanthema, can be due 

 to disturbances in the digestive tract where an auto-intoxica- 

 tion is produced. Exanthema also accompanies many 

 infectious diseases and appears associated with conditions 

 leading to cachexia (lung worm plague of sheep). Finally, 

 mange mites produce eczema. In man certain individuals 

 seem predisposed to eczema. 



Symptoms. — The various pathological changes, such as the 

 papule, vesicle, pustule, etc., in eczema can be noted on the 

 living animal. The process passes through its varied stages 

 rather rapidly, one phase developing out of the other. By 

 lifting the crusts the moist areas over the papillary layer of 



Digitized by Microsoft® 



