682 DISEASES OF THE SKIN. 



development of oxalic acid in the circulation ; and on this 

 account they must not be given in cases of pityriasis. 



In some instances this bran-like scurf seems to be due to a 

 deficient secretion of the sebaceous follicles of the legs and heels, 

 induced by the use of soft soap or very hard water ; however, it 

 is not correctly pityriasis, but erythema, accompanied with fine 

 branny scales. 



Scales also form on various parts of the body, caused by con- 

 tact with ill-fitting harness ; but this is not properly pityriasis, 

 but desquamation of cuticle owing to irritation. 



Pityriasis is distinguished from psoriasis by the absence of 

 tliickening of the derma, by the scales being finer, separating 

 more easily, by their very rapid production, and by the disease 

 not attacking the flexures of the limbs. 



Treatment. — The treatment is to be general, and to consist 

 in the prohibition of all articles of diet calculated to furnish 

 much saccharine matter. A gentle purgative is to be adminis- 

 tered, succeeded b}" the persistent use of pitch internally. The 

 pitch seems to have some influence in preventing the conversion 

 of the starchy and saccharine constituents of the food into 

 oxalic acid. 



Liquid pitch made into a ball of sufficient size, with linseed 

 meal, answers the purpose very well, the dose being regulated 

 by the size of the horse. 



Alkahne lotions may be applied to the skin if the scurf is at 

 all thick ; but, as a rule, the scales speedily separate from the 

 skin, collect on the surface of the hair, and are easily removed 

 with the brush. 



DISOEDERED SENSIBILITY OF THE DERMA. — PRURIGO. 



Prurigo or Pruritis. — The most striking feature of this con- 

 dition is severe itching, and it very often consists of what Mr. 

 Percivall calls " a sort of cutaneous furoi\ to which horses, pam- 

 j)ered and little worked, are liable, and which appears constitu- 

 tional in its origin." 



There is insufferable itching, and the habit, once contracted, 

 is exceedingly difficult to get rid of. 



Cases of this kind must be treated by purgatives, alkalies, and 

 alkaline washes, such as the following : — 



