LICHEN — PRURIGO. 747 



to existing itching, do not exude even serous fluid. On 

 abrasion, however, there may occur a considerable exudation, 

 which somewhat alters their general appearance. On their 

 natural subsidence a full exfoliation of minute epithelial scales 

 takes place, with sometimes a marked heightening of colour in 

 the freshly developed hairs. 



The originally appearing or elementary lesions in the papular 

 inflammation may, in the horse, be fairly Avell embraced by the 

 two recognised forms of skin papulation, lichen and prurigo. 

 Although retaining these terms of comparative pathology, as 

 representing with tolerable accuracy the papulary or plastic 

 inflammatory action ordinarily met with in the horse, it must 

 not be taken for granted that these equine affections are in 

 every respect the analogue and counterpart of similarly named 

 skin diseases in man. ' Both these affections are chronic rather 

 than acute ; and with eczema, in its various developments, may 

 be regarded as representing the pruriginous dermatoses of the 

 horse. 



In the former, the irregularly scattered, sometimes roughly 

 s3Tiimetrical papules, or irritations of the dermal tissues, are 

 smaller, more distinctly accuminated, and less itchy, than in 

 the latter, with which, in addition to the papulation, there is 

 well-marked infiltration and thickening, with distinct coriaceous 

 characters imparted to the skin, and where the itching is alwaj's 

 a jirominent symptom. 



In Lichen, in the horse, the papules are relatively larger 

 than in man, and more resemble the development of ecthyma, 

 only they do not suppurate. By abrasion, both in this and 

 prurigo, there may be much exudation and crusting. In some 

 individual cases, their character of special invasion of the 

 hair-follicles, and their extension by rej)etition of the separate 

 follicular inflammations and excessive cell-proliferation, is 

 very well made out. 



Their course is usually erratic, or rather prolonged, and 

 their resolution is attended with much shedding of bran-like 

 scales. 



In Prurigo, the papules or elevations which result from 

 exudation into the paj)illary layer and the rete, together with 

 hypertrophy of the ej)idermis, are more varied in size and less 

 discrete. Amongst a number of smaller elevations scattered 



