We may here first summarize briefly the characters of the gametes, though the subject is one which requires further elucidation, more especially as to the characters of the young forms. Malignant tertian microgametocyte (male crescent): (1) The nuclear chromatin occurs in an extensive loose network; (2) the protoplasm stains a light blue only; (3) the pigment is scattered; (4) the shape is kidney shaped, shorter, and broader than the female. Macrogametocyte (female crescent): (1) The nuclear chromatin occurs in a compact, dense mass; (2) the protoplasm stains a deep blue; (3) the pigment is collected into masses or small rings; (4) the shape is long, narrow, and typically crescentic. According to Maurer, the young gametes occurring in the circulation are characterized by-(1) Their accurate spheric shape; (2) the protoplasm of the parasite is of the same thickness all round; (3) the nucleus forms a portion of the ring and does not project, as in the schizonts; (4) the absence of coarse stippling in the red cells; (5) around the young gametes there soon develops a circumferential red line of stain, as in the adult forms. Simple tertian microgametocyte: (1) They are smaller than the schizonts and the females; (2) the nuclear chromatin occurs in a loose tangle, centrally placed or extending across the cell, and is separated from (3) by a clear space; (3) the protoplasm may appear greenish, owing to the fact of its being really stained light blue, while the pigment is greenish (Argutinsky); (4) the pigment is coarser than in other forms (this, according to Schaudinn, is only apparently so). Simple tertian macrogamete: (1) They are the largest parasitic forms; (2) the nuclear chromatin is small and homogeneous in character, laterally applied, seldom outlined by a clear space; (3) the protoplasm stains a deep blue; (4) the pigment is smaller in amount and finer than in the males, though Schaudinn says that such differences are apparent only. Quartan gametes: The differences in the gametes of the quartan parasites have been little studied, and, indeed, they are commonly exceedingly scanty in the regular types of quartan fever, probably due to the slight immunity acquired against this form, but presumably the differences are of the same character here as generally in the Sporozoa.
The differences in the characters of the gametes are very readily observed in the case of Halteridium (H. danilewskyi) of birds, and are most suitable for a preliminary study.
The technic of feeding and mode of examining mosquitos for various stages of the parasites we shall describe later (p. 215). We will suppose now that an anopheline had been fed on the blood of a patient containing gametes of the malignant tertian parasites,- i. e., crescents,-and it is as well to have made sure by examining fresh blood that the flagellating forms, viz., the male gametes, are present, for if these are present, the female gametes are also present, but it would seem that the converse is not necessarily true. The midgut is isolated from examples killed at various intervals.
First and second days: Fusiform, spindle shaped bodies are present (vermiculi), which are penetrating the epithelial wall and may have reached the subjacent muscular layer. These spindle bodies have a vacuolated appearance, and the pigment (malarial) is situated for the most part at the blunt end. In stained specimens there is a considerable mass of chromatin centrally placed. Third and fourth days: The parasites have increased in size, the protoplasm is more distinctly reticular or vacuolated, the pigment is collected into little granular clumps, and the whole structure is seen to be definitely encysted. Fifth and sixth days: The parasites now appear as hernias on the external wall of the gut. They may reach 70 micro in diameter (being generally 40 to 50 ft). The pigment in the later stages has almost entirely disappeared, and the cyst contains a number of highly refractile bodies resembling fat granules. Seventh and eighth days: The large, well developed cysts now contain large numbers of thread like bodies, while indications of the formation of these are seen in the previous stage. They radiate from a number of centers. On applying pressure to the specimen the cyst ruptures and large masses of these curved, thread like bodies-the sporozoites -escape into the surrounding fluid. On staining, they are found to possess one or more small masses of nuclear matter centrally placed. They taper at either end, and are about 14 micro in length. If examined in serum, the sporozoites are found to have well marked, writhing movements, and in the case of sporozoites derived from the glands, they were found by Christophers and myself, after remaining under the cover glass overnight, to have changed into bodies indistinguishable from young, "ring form" parasites, though they were not seen to enter blood cells, though these had been added.
In large cysts found in the stomach wall are also found structures the nature of which is perhaps still a matter of doubt. Originally noticed by Ross in the proteosoma cysts in the stomach wall of Culices fed on bird's blood containing these parasites, they were termed by him "brown spores." They were originally thought to represent a still further cycle in the life history of the parasite, and were supposed to be a resistant form capable of carrying on the life of the parasite when the mosquito died and the spores effected their escape into water. But this is purely conjecture, and it seems more likely that they have nothing whatever to do with the parasite but form a quite independent infection of a form of bacterial (or another protozoan) life. These bodies, as described by different observers, vary much in appearance, so that it is evident we have not always the same organism present. Some are typically sausage, or banana shaped and dark brown in color. They are found in cysts in which the sporozoites have disappeared or have been destroyed by their action. These banana like black spores have also been found in the region of the salivary gland, though it could not, in the dissection, be said with certainty that they were in the glands. In thousands of Anophelince dissected by Christophers and myself in India they were encountered only once, and in Africa they were not seen by us. On the other hand, in Italy they appear to be commoner, and their characteristics somewhat different. Thus, in addition to the more or less curved spores, there are others of a brownish yellow color, almost spheric, showing concentric layers. The size of these is also very variable. By the Italians they are considered to be degeneration products of the cyst contents. Furthermore, in these cysts other Sporozoa than the true malarial parasites have been encountered-long oval spores, larger than those which commonly infect the ovaries.