Vesicle

VESICLE (Latin: vesicula - little bladder), a hemispherical protrusion of the skin, from pinhead to pea size, embedded in the thickness of the epidermis. The contents of a V. are usually transparent at first, later becoming cloudy from the admixture of pus, which arises under the influence of pus-forming bacteria penetrating through its covering; more rarely it is reddish from the admixture of blood. The covering of the blister consists of the horny layer or of it and the granular layer, and sometimes also of cells of the prickle cell layer. Blisters lying superficially quickly burst (in eczema), giving an erosion with a moist surface. The cavity of a V., filled with exudate, is sometimes single-chambered through acantholysis (in pemphigus), more often divided by partitions of the Malpighian layer into several chambers (herpes, pemphigus vegetans). Drying, a V. turns into a crust, which then falls off, without leaving a scar.