In 1947, Rebuck1 devised a simple technique for the study of inflammation. After abrasion of the skin, a sterile glass cover slip is applied and allowed to remain in contact with the skin for a variable period of time. The cover slips are removed at intervals throughout a 24-hour period, fixed to a glass slide with clarite or balsam, and stained with Wright-Giemsa. With this technique, one is able to follow the orderly progression of events at the inflammatory site. In normal persons, a highly reproducible sequence of events is observed. Initially, typical polymorphonuclear leukocytes predominate. In the four-six-hour sampling lymphocytes or small mononuclear cells appear in the exudate, and in subsequent samples they are present in increasing numbers. The mononuclear cells appear to develop into hematogenous macrophages between the 8- and 14-hour stages. In the 18- to 24-hour stages, the mononuclear macrophages display increases in cytoplasmic nuclear ratio,