It is rather remarkable that the disease was not noted by so keen an observer as Torti, if it existed in his time, and Manson states that it is strange that it should not have been recognized in India if it had existed there prior to recent times. Some think that its introduction into Africa has been of recent occurrence. There are two explanations of the recent greater prominence of the disease in Africa and other tropical areas, where malignant malaria prevails extensively, which are (1) that there has been a great influx of susceptible Europeans into such areas during the past twenty or thirty years and (2) that the more frequent and excessive dosing of malarial patients with quinine is responsible. [Illustration: FIG. 23.—Geographical distribution of blackwater fever.] =Geographical Distribution.=—It is in tropical Africa that the disease is of prime importance as a cause of death and invaliding. Here it prevails chiefly in West, Central and East Africa from about 12° N. to 12° S. latitude. It is less frequent in Northern Africa although a considerable number of cases have been reported from Algeria. It is unknown in Egypt, a country where malaria is very rare in Europeans. In India it occurs in several districts and Stephens states that in the Duars (Bengal) he saw more cases in a fortnight than he had seen in the same time in Africa. In Europe it occurs chiefly in Southern Italy, Sicily, Sardinia and Greece. Blackwater fever was frequently noted among the British forces in Macedonia and Palestine during the World War. It is common in Central America and Northern South America, especially in the regions of the Amazon basin, in Brazil. In the U. S. it is chiefly found in the most malarious sections of Arkansas, Mississippi, Louisiana, Texas, Alabama, Georgia, Florida and South Carolina. It would seem that it is becoming more rare in the Southern States. As a result of malarial prophylaxis among the Americans working in the Panama Canal Zone it has almost disappeared among them although still common among the white Europeans in the same region who neglect quinine prophylaxis and mosquito protection. ETIOLOGY AND EPIDEMIOLOGY =Etiology.=—There seem to be cases where from very heavy infection with the malignant tertian parasite, as from 12 to 20% of the red cells, one can expect the appearance of a more or less dark urine, the color of which is due to haemoglobinuria. Such cases give support to the old view that haemoglobinuric fever was simply a type of pernicious malaria. Brem has proposed for such cases the designation, pernicious malarial fever with haemoglobinuria.