342 MORBID ANATOMY OF THE SKIN. 



Pompliosis, as a transient oedema of the papillary body, in- 

 terferes less with the nutritive processes in the skin than any 

 other exanthem ; it is never followed by any more profound 

 disorder ; seldom even by branny desquamation of the cuticle. 



Among the external irritants best adapted to produce this 

 eruption are the sting of the nettle and that of some insects ; 

 among internal ones certain articles of diet (strawberries) and 

 the specific cause of nettle-fever (Nesselfieber). 



§ 291. — 4. The vesicular or bullous exanthem. The papule 

 and the wheal showed us the exudation arrested in the peri- 

 vascular connective tissue, on its way from the capillaries of 

 the papillary body to the surface of the skin. The vesicle 

 or bulla takes us a step farther. The exudation is now in the 

 substance of the epidermis ; it accumulates between the mucous 

 and the horny layers ; the latter is raised and arched out- 

 wards like a knob. The terms ^^ vesicula " and " bulla " are 

 both employed to designate this condition; their difference is 

 one of degree only. The Aesicle includes those which are not 

 bigger than millet-seeds ; the bulla includes all which exceed 

 this size. 



A vesicle may be broadly said to originate in the transuda- 

 tion of a fluid from the vessels, which forces its way up from the 

 distended capillaries of the papillary body, passes through the 

 rete mucosum, and is arrested by the horny lamina. The cells 

 of the latter are so firmly united, partly by the close way in 

 which they are packed together, partly too by a sort of sutural 

 connexion of their channelled surfaces, that they form a con- 

 tinuous tough membrane, impermeable to fluid, and well adapted 

 for retaining and roofing in e^en larger quantities of it. The 

 mucous layer is variously afl^ected in diflerent cases. If a bleb 

 is developed very rapidly, as e.g. in gangrene, the soft bodies of 

 the cells are mechanically stretched into slender threads by the 

 force of the transuding current — threads which give a mossy 

 roughness to the surface of the papillary body. Should the 

 transudation take place more slowly, as" in Herpes and Ery- 

 sipelas bullosum (Haic/ht), the deepest layer of the rete Malpighii 

 remains unaltered, while the " intermediate" epithelium-cells are 

 partly detached, partly pushed aside. The transuded fluid wells 

 up with greater force from the apices of the papillae than from 

 the interpapillary furrows ; hence the layer of cells above 



