266 DISEASES OF THE SKIN 



which are interwoven to form mycelia and large, round, light- 

 refracting spores which predominate. The fungus lives in 

 the hair sac, where it produces an inflammation of the hair 

 follicle, causing the hair to fall out, and also within the hair 

 shaft, which it makes brittle, causing it to break off. In- 

 fection is spread by direct contact or through intermediary 

 agents, such as posts, stall partitions, etc., against which 

 affected animals have rubbed themselves. Harness, saddles, 

 and grooming utensils are also carriers. 



Forms. — Four forms of herpes tonsurans are distinguished 

 clinically, depending upon the species of animals attacked and 

 the location and age of the lesion: (a) Herpes tonsurans 

 which is characterized by round bald spots without inflam- 

 mation of the skin. 



(b) Herpes circinatus, the centre healing but the periphery 

 remaining diseased thus forming a hoop-shaped, circular 

 lesion — hence the name "ringworm." (c) Herpes maculosis, 

 occurring on the skin of old animals and leading to alopecia 

 and a superficial chronic dermatitis with desquamation of 

 the epidermis which forms slate-gray-colored, asbestos-like 

 scales, (d) Herpes vesiculosus which attacks the thin skin of 

 young animals (calves, lambs). This is a dermatitis with 

 vesicle formation. The vesicles soon rupture forming thick 

 yellow scaly scabs or crusts in the neighborhood of the mouth, 

 face and eyes. 



Cattle. — In adult cattle herpes usually attacks first the 

 head and neck, where it forms small, well-defined, round bald 

 spots which by confluence may reach the size of an open 

 hand. These areas are covered with grayish-white, asbestos- 

 like crusts. On black skin the crusts are thicker than on 

 white. The skin is sometimes thickened and creviced. 

 Healing usually takes place under the crusts in two or three 

 months. When there is much pruritus, causing rubbing and 

 scratching, secondary lesions form, prolonging the course of 

 the disease several months. 



Diagnosis. — A positive diagnosis can be made only with the 

 microscope. In sucking calves herpes attacks the skin around 

 the mouth. There appear round spots covered with yellowish 

 scabs made up of bran-like scales. 



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