While in charge of the laboratory of the military hospital in Cebu, P. I. (Captain Kulp) it was my duty to examine the blood of all malarial and dengue patients. An epidemic of the latter disease occurred during December, 1905, and lasted about six weeks. No malarial parasites were found, but I observed in nearly every case very active, small (about 2 micron), round translucent bodies, with clearly defined edges, very motile, and easily visible with a 1/6 objective, but better with 1/12 oil immersion lens. They were seldom or never found in the erythrocytes, but often on them, as well as free in the plasma. They appeared about the second day of the fever, and could never be found after the temperature became permanently normal or after the administration of quinin. They sometimes remained active for as long a period as an hour and three-quarters. Unfortunately, the epidemic ceased