ECZEMA. 



46T 



in eczemas of very small extent ; and, on the other hand, it differs in 

 the irregularity of its course, which, unlike that of herpes, is not con- 

 fined to any fixed period of time. Eczema may be regarded as the 

 analogue of catarrh. It is the most common of all diseases of the 

 skin, just as catarrh is the most common affection of the mucous mem- 

 branes. Like catarrh, too, it is a disease of the surface rather than of 

 the parenchyma, and it is accompanied by a profuse superficial serous 

 transudation. It also usually involves wide tracts of the skin, or, if 

 its area be small, it shows a tendency to spread. 



Eczema being a diffuse dermatitis, with superficial serous exuda- 

 tion, it is plain that the formation of vesicles must be a frequent oc- 

 currence in this disease ; but it is equally certain that the presence of 

 vesicles is by no means one of its constant or essential symptoms. If 

 the superficial exudation be profuse enough to form small drops, and 

 if the epidermis possess sufficient resisting power, not to give way im- 

 mediately before it, vesicles form, producing the variety of eczema 

 known as eczema simplex, seu vesiculosum. When there is a profuse 

 admixture of young cells with the contents of the vesicles (which 

 always contain a few such cells), so that the serum is turbid, yellow, 

 and purulent, the vesicles become pustules, and the disease is, called 

 eczema impetiyinosum. When the transudation is not so copious 

 as to elevate or to break through the epidermis, it usually soon dries 

 up ; and then, instead of vesicles or pustules, nothing is to be seen 

 except dry scales rising from the reddened skin. This has been 

 called pityriasis rubra, and is now known as eczema squamosum. 



From its anatomical and pathological point of view, I cannot 

 regard the form of pityriasis rubra, which Helra considers as dis- 

 tinct from eczema squamosum, as any thing more than a squamous 

 eczema capable of endangering life from its superficial extent. Ac- 

 cording to Hebrtfs description, this affection is also a superficial 

 dermatitis, whose scanty superficial exudation, mingled with epi- 

 dermic cells, dries into scales, and which, like all exanthemata in- 

 volving the whole surface, is a dangerous disease. 



Finally, when the exudation detaches the epidermis so as to deprive 

 the red, moist corium of its covering, and expose it to view, it is called 

 eczema rubrum (" salt rheum "). After the epidermis has disappeared, 

 the exudation upon the surface often dries up into scabs and crusts, 

 whence many other names formerly applied to moist eczema were 

 derived, such as tinece or crustce lactece, granulatce, mucosce, etc., etc. 

 Hebra also counts that form of eruption as an eczema which is usually 

 called lichen, and which appears as a rash of solid papules. He thus 

 adds a fifth species, eczema papulosum, to the series. Since a serous 

 exudation is also thrown out upon the surface in the papular erup- 



