LICHEN. 489 



oppression occurs in the region of the stomach, or when tears begin to 

 flow from the eyes, the treatment is to be suspended for a few days. 

 Cantharides, the antimonials, anthracokali, tar-pills, and other articles, 

 formerly in vogue, having proved themselves worthless in treatment 

 of psoriasis, have very justly been abandoned of late years. However, 

 hi plethoric, vigorous subjects, the cure may be accelerated by restrict- 

 ing the diet, and by combining the use of laxative tisanes with the 

 specific treatment; for we know that such measures alone, when 

 pushed vigorously, will cause a psoriasis to disappear. 



CHAPTER XIII. 



LICHEN DERMATITIS FORMING GROUPS OF PERSISTENT CONICAL 



NODULES. 



ETIOLOGY. In lichen, instead of the appearance of vesicles, filled 

 with serum, upon the skin, there is an eruption of solid nodules (papu- 

 lae). The exudation which forms in this disease infiltrates the cutis, 

 and produces a circumscribed swelling of its parenchyma, but the por- 

 tion of it effused upon the free surface of the cutis is only sufficient lo 

 swell the cells of the rete Malpighii, and to loosen the layer of epider- 

 mis above it. This is why lichen terminates by desquamation. It 

 is only in a few cases that the source of lichen can be traced to the 

 action of slight external irritants ; for instance, to the bites of parasites, 

 to chafing of the skin by roughness of the clothing, to the effect of 

 dirt, or to the influence of high temperature. In most cases we can- 

 not tell why the numerous small circumscribed portions of the cutis, 

 of which the lichen-knots consist, should be thus affected, while the 

 rest of the skin about them appears sound. Lichen is especially com- 

 mon among scrofulous persons. 



SYMPTOMS AND COURSE. Lichen is characterized by nodules of 

 about the size of a millet-seed. They are of normal color, or else of a 

 pale, yellowish red ; sometimes they are even paler than the surround 

 ing skin. In the latter case, the blood-vessels, from which the exuda 

 tion originally proceeded, have afterward been compressed by the exu 

 dation. The nodules usually form groups ; sometimes they only ap 

 pear upon particular regions of the body ; at others, they spread ove 

 a wider extent of surface. In the milder forms of lichen (lichen sim 

 plex), the papules itch but slightly, or give no annoyance whatever, 

 and only last for a short time. They disappear in a week or two, and, 

 after desquamation of the epidermis covering the papules, the disease 

 usually terminates. More rarely, lichen simplex assumes a chronic 

 form, fresh eruptions of the nodules following one another in rapid 



