Plasmodium Ovale Considered as a Modification of Plasmodium Vivax after a Long Residence in the Human Host

In 1922, Stephens observed a patient in a London hospital, suffering from a tertian fever in whose blood he found a plasmodium similar to Plasmodium malariae but the infected erythrocytes showed Schuffner's dots and were often of an oval shape. This investigator considered the plasmodium as a new species and called it Plasmodium ovale. The clinical history of the patient was briefly as follows:In December, 1916, contracted malaria in East Africa. January, 1918, left East Africa. April 8 to 11, 1918, and April 27 to May 4, 1918, the blood films which are still preserved, made for the purpose of counting the leucocytes, showed simple tertian parasites. July 18 to July 20, 1918, the blood films, still in existence, showed simple tertian parasites. July 21 to 27, 1918, the entry made in the card index was “negative.” July 28, 1918, the entry was “?simple tertian.” July 29, 1918, the entry was “? simple tertian, ? quartan.”