448 DISEASES OP THE SKIN. 



ting it in post-mortem examination, a striking diminution of its thick 

 ness will be observed. A coating of detached scales of epidermis is 

 usually found upon the skin of such subjects. This is not a product 

 of any coexisting hypertrophy of the epidermic layer, but has formed 

 simply because the cutaneous secretion is diminished, which keeps the 

 skin pliable during health, and which causes the epidermis of healthy 

 persons to fall imperceptibly. In other words, in the so-called pityriasis 

 tabescentium the epidermic cells are not generated in undue quantity, 

 but they are shed in a more conspicuous manner than is natural to a 

 person in good health. Atrophy of the skin may also proceed from 

 continued pressure either from within or from without. We have al- 

 ready said that a corn induces partial atrophy of the corium. Favus 

 crusts and scabs, which have adhered to the skin for a long time, have 

 a similar effect. As pressure from without sometimes injures the pap- 

 illary layer of the skin, the product of the latter, the epidermic cells, 

 is formed in diminished quantity, and hence the cuticle over the com- 

 pressed point is remarkably thin. The effect is different when the 

 pressure upon the skin proceeds from within, as, for instance, in the 

 great distention of the belly which occurs in pregnancy or during 

 dropsical effusion, and in cases of excessive swelling of other parts of 

 the body covered by skin. In such cases it is the deeper layers of the 

 corium and the glandular structure of the skin which suffer, the pro- 

 duction of epidermis not undergoing any derangement. I have no 

 doubt that the pityriasis of the abdomen and extremities consequent 

 upon repeated pregnancy and extensive dropsy, as well as pityriasis 

 tabescentium, is attributable to atrophy of the deeper layers of the 

 corium and cutaneous glands, with abnormal dryness of the epidermis. 



A congenital absence of pigment throughout the rete Malpighii of 

 the whole body occurs in albinos. Sometimes from unknown causes 

 the pigment disappears from circumscribed patches of skin. These 

 spots are of a milky whiteness, and, as they most frequently occur in 

 individuals of a strongly-marked brunette complexion, they create a 

 striking contrast with the surrounding surface (vitiligo, achroma). 



The hair-follicles often undergo atrophy, particularly the follicles 

 of the scalp, and, in consequence of this, the hair falls off. If the 

 atrophy does not cause complete destruction of the hair-bulb, the pro- 

 duction of hair does not cease entirely, but the wasted follicles can only 

 produce a fine woolly down, instead of vigorous normal hair. Bald- 

 headed persons, finding this downy growth upon their heads, are often 

 inspired with fallacious hopes, especially if just before they have been 

 using the " eau de lob " or " lion-pomade," and have faith in the tales 

 told of these articles. Baldness arising from atrophy of the hair-bulbs is 

 called calvities, or calvities senilis, from its liability to occur in old per 



