VARICELLA, or Varicella lymphatica, is the eruptive disease com monly called chickenpox, and which has been described by different writers under the names of chrystalli, variolce, =rioter, spuricr, &c. It is almost peculiar to infants and young children ; and tho eruption appears either without premonitory signs, or after two or three days of slight illness. The eruption commences on the shoulders, neck, and breast : on the scalp and back it is usually abundant, but the face is only slightly affected. It consists of vesicles, about as largo as a split-pea, full of transparent fluid, and lenticular, conoid, or globular in their form. They are surrounded by a slight superficial redness, and successive crops of them appear for two or three days, the old vesicles shrivelling up as the new ones are formed. Most of the vesicles burst naturally, and the cuticle which covered them falls to the level of the surrounding skin ; but some shrink, the fluid within them becoming whey-like, or, if they be much irritated, purulent. After drying they form small scabs, which fall off in grains, and sometimes leave small superficial scars. The whole course of the disease occupies about a
week, and is not attended by any important constitutional disturbance. It therefore requires no particular treatment.
The first writers on varicella considered it as only a mild form of variola, or small-pox, and the same view is maintained by some modern authors, especially by Dr. Thomson of Edinburgh. It is however more probable that chicken-pox and small-pox are essentially different, on these grounds : 1. They sometimes prevail in distinct epidemics, no case of genuine small-pox occurring among many of chicken-pox.
2. The characters of the chicken-pox eruption are altogether different from those of small-pox, even in its mildest and most modified form.
3. Chicken-pox is not inoculable, though the mildest small-pox is.
4. Chicken-pox is altogether unaffected by previous vaccination, and does not prevent the action of vaccine matter.