THE SPECIES OF MALARIAL PARASITES OF MAN.
In view of the differences in opinion regarding “species” and “varieties,” the dispute whether the malarial parasites of man represent one species with several varieties, or several species is almost superfluous. If necessary two genera may be distinguished.
The parasites of the tertian and quartan fever are alike in that their gametocytes have a rounded shape (figs. 80, _12_, _13_), whilst the corresponding stages of the pernicious or malignant tertian parasites are crescentic (figs. 81, 88). These differences are used by some writers as the distinguishing characteristic of two genera: _Plasmodium_, Marchiafava and Celli, 1885, for the first mentioned species; _Laverania_, Grassi and Feletti, 1889, for the pernicious or malignant tertian parasite. Whether there is a genuine quotidian fever and accordingly a special quotidian parasite is still disputed.
These parasites are treated in practical detail in Stephens and Christophers’ “Practical Study of Malaria,” 3rd edition, 1908.
*Plasmodium vivax*, Grassi and Feletti, 1890.
Syn.: _Hæmamœba vivax_, Grassi and Feletti, 1890; _Plasmodium malariæ_ var. _tertianæ_, Celli and Sanfelice, 1891; _Hæmamœba laverani_ var. _tertiana_, Labbé, 1894; *Hæmosporidium tertianum*, Lewkowitz, 1897; _Plasmodium malariæ tertianum_, Labbé, 1899: _Hæmamœba malariæ_ var. _magna_, Laveran, 1900, p.p.; _Hæmamœba malariæ_ var. _tertianæ_, Laveran, 1901.
This species, _P. vivax_,[201] is the causal agent of the simple or spring tertian fever and is, therefore, named directly the tertian or benign tertian parasite (figs. 80, _3_-_8_; 85). During the afebrile period in the patient, the young trophozoites or amœbulæ appear on or in the red blood corpuscles as pale bodies of 1·5 µ to 2 µ diameter which at first show only slow amœboid movements. Their nucleus is difficult to recognize in the early stage. Soon the food vacuole is formed and this grows concomitantly with the trophozoite and the parasite has a ring-like appearance. Afterwards the vacuole diminishes, and at this period the first brownish melanin granule appears. From this time the activity and number of the pigment granules increase with continuous growth. When the parasite has grown to about one-third the diameter of the erythrocyte the latter shows characteristic red Schüffner’s dots or “fine stippling,” after staining with Romanowsky’s solution. Later, after about twenty-four hours, the blood corpuscles begin to grow pale, then to increase in size, and after thirty-six hours, that is, about twelve hours before the next attack of fever, schizogony of the parasite is initiated by the division of the nucleus. The parasite at this time occupies half to two-thirds of the enlarged blood corpuscle. The daughter nuclei continue dividing until sixteen, and occasionally twenty-four, daughter nuclei are produced. The pigment which, up till now lies nearer the periphery, moves to the middle, while the nuclei lie nearer the surface.