VEGETABLE PARASITIC SKIX DISEASES. 787 



B. DERMATOPHYTIC, EPIPHYTIC, OR VEGETABLE PARASITIC 

 SKIN DISEASES. 



The group of vegetable parasitic diseases of tlie skin in the 

 horse is represented by one, or probably by two, of the so-called 

 tinecc. 



(a) Tinea Tonsurans — Tinea Circinata — Ringworm Proper. 



This, in the horse, is the better known and more frequently 

 occurring of the tinea), and it may be regarded as typical of the 

 entire group. 



Definition. — An a feet ion of the hairs, the hair-sheaths and 

 cells of the epidermis over different 2^ccrts of the hody, usually 

 occupying circibmscrihed circular spots or patches, lohich start 

 into existence by slight elevations of the sujjerficial cuticulav 

 scales, and attended ivith an altered brittle condition of the 

 hair, slight itching, and the presence of a peculiar cryptogam, 

 the Achorion vel Tricophyton tonsurans. 



Pathology, a. Nature. — The existence and nature of this 

 affection is evidently closely bound up with the life and deve- 

 lopment of the peculiar fungus which is inseparably associated 

 with it. This parasite, which consists chiefly of spores or 

 conidia of an oval or round form, often separate and disjoined, 

 but occasionally joined or linked together, and a small amount 

 of elongated tubular matter, apparently invades the interior of 

 the root and shaft of the hair. These, when affected, undergo 

 certain recognised changes; they swell or increase in bulk, 

 losing colour, becoming opaque and brittle, ultimately break- 

 ing across, and appear frayed at the point of fracture, their 

 interior at the same time becoming more rapidly iilled with 

 sporules, granular matter, and mycelium, in this way giving a 

 certain asperity to the surface. At the same time the super- 

 ficial layers of the epidermis become raised from the growth 

 beneath of the fungus ; by this raising they possess a clear 

 grey and shining character, 



b. Causation. — The immediate cause of this disturbance is 

 the implantation of the spores or seeds of the fungus into the 

 hair-follicle of the healthy skin. At the same time there 

 seems a certainty that a marked receptivity and accommoda- 



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