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DISEASES OF THE SKIN. 



By the expressions phyma or dermatoma we designate more or 

 less salient cutaneous neoformations, which are active and obstinate. 



Squamce are epidermic lamellae which become detached from the 

 cutaneous surface (desquamation) in the shape of small pellicles or 

 thicker scales. 



Scabs are masses resulting from desiccation on the surface of the 

 skin — pus, serum, and blood which has been extravasated. 



By maculœ we designate the pigmentary spots which persist for 

 more or less time after the different eruptions, or which appear at 

 an advanced stage of their evolution. 



Cicatrices are small islands of newly-formed tissue which fill the 

 losses of the dermic substance. 



The expression rash is obsolete nowadays, and was applied ta 

 cutaneous diseases of chronic course giving origin to crusts and 

 cutaneous exfoliations.] 



I. NON-PARASITIC SKIN DISEASES. 



ERYTHEMA: ERYTHEMATOUS DERMATITIS. 



Erythema of the skin — hyperemia of the papillary layer and 

 superficial capillaries — is the simplest of tegumentary diseases.. 

 Sometimes it is diffuse, at other times more or less circumscribed 

 (roseola). In our large domestic animals it is only found upon the 

 depigmented cutaneous surfaces (upon the white spots of the head 

 and extremities in those animals the skin of which does not con- 

 tain any pigment (sheep, pig, dog, albino or piebald horses, etc.), 

 it may be found upon the most diverse regions. Its only remark- 

 able symptom is a diffuse or circumscribed redness of the skin,, 

 which disappears momentarily through the pressure of the finger, 

 contrary to what takes place when this abnormal coloration is of 

 hemorrhagic nature (peteohise, ecchymoses, purpura); it is some- 

 times accompanied by pruritus. When it persists for a certain 

 time it leads to an abundant epithelial degeneration. 



Etiology. Erythema sometimes originates quite suddenly and 

 constitutes a real morbid entity, at other times it is but the initial 

 stage of other cutaneous diseases. In the first case it is ordinarily 

 fugacious and does not leave any anatomical alteration behind it. 



The principal causes are : 



1. Mechanical irritations of the skin [pressures, frictions, shear- 



