with a specific disease of man was the ameba discovered by Lambl (1860), first observed in the human intestine by Lösch in 1875, and said by the latter to be the cause of amebic dysentery. In 1891 Councilman and Lafleur, after a very accurate study of this disease, as it occurred in Baltimore, came to the conclusion that two types of amebse must be recognized; one, the Ameba coli, was harmless, another, which they called Ameba dysenteriæ, they claimed to be the cause of tropical dysentery. In this view they were supported later by the feeding experiments of Casagrandi and Barbagallo (1897) and of Schaudinn (1903); the latter also introduced the name Entameba histolytica for the pathogenic form, and Entameba coli for the harmless form. It has since been found that two forms of tropical dysentery exist, one of which, as shown by Shiga, Kruse and Flexner, is due to bacteria—but equally definitely has the etiology of an amebic form been established.
In the meantime another protozoan disease was being investigated. Laveran, a French military physician, stationed in Algiers, announced in 1880 that the dancing pigmented bodies frequently seen in the red blood cells in malaria were altered hemoglobin granules within a protozoon to which he gave the name Oscillaria malariæ. This name was altered by Marchiafava and Celli to Plasmodium malariæ, in 1885, and Golgi, in 1886, by demonstrating that the characteristic paroxysms of the disease coincide with the segmentation or sporulation of this parasite, settled definitely the question of its etiologic relation to malaria.
The work on malaria constituted a very large part of the activity in medical investigation at this time. Until the middle of the nineties, many investigators were interesting themselves in the study of the different forms of parasites concerned, their life history and the methods for demonstrating them; these activities, with the study of similar parasites in birds, gave a great impetus to the study of pathogenic protozoa, and prepared many workers for a wider field.
Nevertheless, but few were prepared for the wonderful announcement by Smith and Kilbourne, in 1893, of the transmission of a protozoan disease through a blood-sucking insect. In this, the work of our own countrymen, on a malaria-like disease of cattle, Texas fever, the tick was shown to be the carrier of the Pirosplasma bigeminum, the organism responsible for the disease. The importance of this observation can not be over-estimated. It was the finger-post indicating the way to progress in the study of the transmission, and therefore of the prevention, of protozoan disease, and to Smith and Kilbourne belongs the credit of this great advance, which, it must be admitted, had a great influence on the study of the transmission of malaria and yellow fever. Many suggestions had been made from time to time that these diseases might be due to transmission by the mosquito; and these theories became indisputable fact when Ross announced from India in 1897-99