INTRODUCTION. Histoplasmosis1is a term applied to a fatal infection by a protozoon,Histoplasma capsulatum, which has been encountered three times during the past two and one-half years in Ancon Hospital, Canal Zone, Panama. Clinically and pathologically the disease is suggestive of kala-azar,2a disease of India, characterized by irregular fever, emaciation and splenomegaly and by the presence of the Leishman-Donovan body in the tissues. The micro-organism responsible for the Isthmian infection is different from the Leishman-Donovan body, sufficiently so to warrant its being placed in a different order. The condition was not discovered until the autopsies, and chiefly on that account cultural experiments were unsuccessful and clinical data meager. HISTORICAL SKETCH. Cunningham3published in 1885 an account of bodies found in the tissue obtained from a Delhi boil. Cunningham's technic was crude and the bodies measured 8.8 to 12.6 microns—altogether too large to be the bodies