Cellular reactions in inflammed areas were observed on coverslips. After an initial granulomonocytic phase a massive infiltration by lymphocytes took place. These lymphocytes rapidly hypertrophy and become "mononuclear," "epitheloid" and even giant cells. By injecting 15 to 30 millions of these cells from tularin- (tuberculin) positive donors to negative recipients, allergy of the delayed type is specifically transferred as with lymphocytes. The function of the lymphocyte is discussed on the basis of these findings.