The suspicion that malaria was caused by a living contagium has been entertained from the most ancient times and repeatedly expressed by even the oldest writers (Vitruvius, Varro, Columella).

Lancisi considered the emanations of swamps to be carriers of small animal organisms and eggs, which gained entrance to the body by way of the respiratory or digestive tract. Lancisi pictured to himself an infection of the body by small worms, and advised the examination of the fresh blood, though he confesses that he himself, neither in abscesses (spontaneous nor artificially produced) nor in the gastro intestinal tract of fatal fever cases found worms that were out of the common.

During the decline of the last century, to which medical science owes so much, the question of the parasitic etiology was vigorously pushed and finally successfully proved. Rasorr declared for the parasitic theory in 1842; Mitchell, in 1849. These declarations were followed by numerous painstaking investigations of the air, the water, and the soil of malarial regions, and of the secretions and excretions of patients, with the result that a series of vegetable and animal organisms were brought forward as excitants of the disease. The names of these pioneers will always hold an honorable place in the history of medicine, even though their efforts were in vain: "In magnis et voluisse sat." We may name Hammond, Lemaire, Salisbury, Eklund, Klebs, Tommasi-Crudeli. Still we will refrain from discussing their discoveries and theories, since the investigation of the last eighteen years has shown that their findings were delusions and that the true discovery belongs to a more fortunate master. This is A. Laveran.

The discovery of the malarial parasites by Laveran took place on November 6, 1880. This investigator found himself, at the time, in service in Constantine, a markedly infected malarial station in Algeria, and, taking advantage of the favorable opportunity, he endeavored to revise anew the pathologic anatomy of the disease. He began the study by investigating the formation of the pigment in the organism.

* We introduce here only what is of importance to the clinician, and for further study must refer to the special works of Laveran, "Du paludisme et de son hemato zoaire," Paris, Masson, 1891; Marchiafava and Bignami, "Sulle febbri estivo au tunnali," Rome, Loescher, 1892; Mannaberg, "Die Malariaparasiten," Vienna, Holder, 1893; Thayer and Hewetson, "The Malarial Fevers of Baltimore," Baltimore, the Johns Hopkins Press, 1895.

A logical, as well as fortunate, idea induced him to study the pigment in the blood of the living patient in order to complete the findings in the vascular system of the cadaver. Although previous to this time many other investigators had studied microscopically the blood of malarial patients and recognized therein certain pigment containing bodies which could be differentiated from the pigment carrying leukocytes, Laveran was the first to conjecture the parasitic nature of these bodies and convince himself of it by a long investigation. This new explanation of previously recognized pictures, passed over without presentiment by numerous observers since Hein rich Meckel, is the more creditable to Laveran since his discovery occurred at a time when the Klebs-Tommasi-Crucleli Bacillus malariae (confirmed, as it was, by many) seemed to have determined the etiology of the disease. Laveran found his conjecture, that the hyaline pigmented corpuscles were parasites, confirmed when he observed, on November 6, 1880, several long flagella escape from such a corpuscle and pass across the specimen with lively, whip like movements. On account of their flagellar shape, he considered that they belonged to the genus Oscillaria, and proposed for them the name of Oscillaria malariae. It was only later that these motile bodies were properly classified with the protozoa, among the lowest animals. Laveran's discovery was at first confirmed only by his colleague, Richard.

The bodies which Laveran claimed to be parasites were for years described by other writers as phenomena of degeneration in the red blood corpuscles, and this opinion was even until very recently held by isolated individuals.

The general recognition of Laveran's discovery may be elated from 1885, when his investigations were confirmed by Italian observers, especially Marchiafava and Celli. In addition to these two names, we must not omit that of Golgi, who determined the connection between the fever symptoms and the different stages of development of the hematozoa, on the one hand, and between the fever types and forms of parasites, on the other. It was owing to his clever comprehension that the numerous forms brought to light by other observers without attention to their biologic and clinical significance were separated and placed in their natural relations. Following the methods which he applied to the quartan and tertian fevers, Marchiafava and

Celli, Canalis, Bignami, and others have endeavored to put under the same rules the pernicious summer and autumn types.

Golgi's investigation, moreover, brought up the question of the unity or multiplicity of the malaria micro organism, one of the most interesting and important since Laveran's discovery, though thus far there is little unanimity of view in regard to it.

At the same time attention was directed by Celli and Guarnieri, Grassi and Feletti, the author, Romanowsky, Sakharoff, Ziemann, and others, to a second very important consideration, namely, the structure of the parasites. Omitting details, this question is practically settled.

A further problem arose in relation to how quinin acted, in consideration of the new teaching. The majority of the investigators already mentioned took this up, and it, too, seems to be satisfactorily determined.

Recently the greatest interest has centered in the question of the existence of the parasites in the external world, and their mode of entrance into the human organism. How, too, this problem has been solved, we will see later.

By a fortunate coincidence, shortly after Laveran's discovery, Gaule found in frog's blood, Danilewsky in the blood of lizards, turtles, and certain birds, hemoparasites that, morphologically, showed a striking similarity to the malarial parasites of man.