SQUAMOUS EXANTHEil. 355 



§ 299. — 6. The squamous (wanthcm. I have referred on 

 more than one occasion to the difficulties which beset our path 

 whenever we try to separate the conception of inflammation from 

 that of hypertrophy, as cetiological categories of morbid growth. 

 The squamous exanthem undoubtedly originates in a chronic 

 inflammation of circumscribed portions of the skin. These arc 

 reddened, slightly swollen, and endowed with all the other attri- 

 butes of inflammatory hyperasmia ; the result of this hypera3mic 

 condition being, not an exudation into or under the epidermis, 

 but merely an over-production of perfectly normal epidermic 

 elements. This begins as an increased desquamation of horny 

 eells, of " cuticular scales," upon the hypersemic, slightly raised 

 patch of skin (squama^^ desquamation squamous exanthem). The 

 secretion of cells however, soon assumes greater proportions ; 

 white masses varying in size from a millet-seed to a lentil, and 

 also discoidal plates, are formed, consisting of scales heaped up 

 on one another, and firmly adherent to the parts beneath them 

 (Psoriasis). Why, as the disease progresses, the epidermic cells 

 cease to be simply cast off, why they should accumulate in thick 

 scales, is elucidated by pathological histology as follows. The 

 more exuberant tlie production of cells on the surface of the 

 inflamed cutis, the more imperfect is the degree of development 

 attained by each individual cell. The average height to which 

 their development proceeds under such circumstances is that of 

 the '^ intermediate cells," between the cylindrical elements of 

 the mucous layer and the deeper cells of the horny lamina. 

 That systematic hardening which we call " cornification," re- 

 mains in abeyance ; in its place we have a simple desiccation of 

 the soft protoplasm. During this desiccation the cells very 

 naturally adhere to one another, and thus retain their connexion 

 (which is purely mechanical) with the surflico of the body for a 

 longer period. 



The silvery hue of the scales in psoriasis is due to the 

 admission of air into their substance, simultaneously w^ith the 

 desiccation of their cells ; and this also giv^es them their pecu- 

 liarly spongy and porous consistency. If we pick off" the mass 

 of scales, which may be done as a rule without employing much 

 force, we find the papillary body under it almost entirely bare. 

 The layer of epithelium which protects it is so thin that the least 

 touch is enough to detach it, and to make the surface bleed : we 



