Chicken Pox (varicella), an exanthematous disease, characterized by the eruption of small vesicles appearing in successive crops. It is confined almost exclusively to children. The eruption is preceded by more or less fever for a day or two; it appears first on the back, neck, and breast, whence it spreads to the face, limbs, and body. The eruption is very early, if not from the beginning, vesicular, resembling drops of water about the size of split peas, the contained fluid being transparent or straw-colored; they sometimes run together, and assume a conical or globular form, which has given rise to the described varieties; they are usually surrounded by slight redness, and accompanied by considerable itching, which causes them to be very soon broken. About the fifth day they begin to dry up in scales, which fall off in a few days, leaving a discoloration and sometimes a slight permanent pitting of the skin. Sometimes the contents of the vesicles become pustular, accompanied by higher and more lasting fever; English writers call such cases swine pox.

The Latin name varicella is a diminutive of variola (smallpox), from the opinion which formerly prevailed that the two diseases were nearly allied, variola, varioloid, and varicella being all considered varieties of smallpox; but chicken pox is now understood to be a distinct affection. It may be distinguished from smallpox by its mildness, vesicular character, and the successive appearance of its eruption; though some severe cases are with difficulty distinguished from mild varioloid. It occurs in persons who have been vaccinated and who have had smallpox, and in those who have not experienced vaccination, varioloid, or variola; though often prevalent at the same time with variola, it has not been known to communicate the varioloid or the smallpox; it is not certain that it can be transmitted by inoculation, and it is generally considered very slightly, if at all, contagious. It is a disease unattended with danger, unless from accidental complications, and requires no treatment other than attention to diet, mild laxatives, and cooling drinks.