| PLATE VII |
| EXPLANATION OF PLATE VII |
|
Various forms of
malarial parasites (Thayer and Hewetson). 1 to 10, inclusive, Tertian organisms; 11 to 17, inclusive, quartan organisms; 18 to 27, inclusive, estivo-autumnal organisms; 1, young hyaline form; 2, hyaline form with beginning pigmentation; 3, pigmented form; 4, full-grown pigmented form; 5, 6, 7, 8, segmenting forms; 9, extracellular pigmented form; 10, flagellate form; 11, young hyaline form; 12, 13, pigmented forms; 14, fully developed pigmented form; 15, 16, segmenting forms; 17, flagellate form; 18, 19, 20, ring-like and cross-like hyaline forms; 21, 22, pigmented forms; 23, 24, segmenting forms; 25, 26, 27, crescents. |
(b) In Stained Films ([Plate VI]).—Recognition of the parasite, especially the young forms, is much easier in films stained by Wright's or some similar stain than in fresh blood. When very scarce, they may sometimes be found, although their structure is not well shown, by the method of Ruge. This consists in spreading a very thick layer of blood, drying, placing for a few minutes in a fluid containing 5 per cent. formalin and 1 per cent. acetic acid, which removes the hemoglobin and fixes the smear, rinsing, drying, and finally staining. If Wright's stain be used in this method, it is recommended that the preparation be subsequently stained for a half-minute with borax-methylene-blue (borax, 5; methylene-blue, 2; water, 100).
In films which are properly stained with Wright's fluid the young organisms are small, round, ring-like or irregular, sky-blue bodies, each with a very small, sharply defined, reddish-purple chromatin mass. Many structures—deposits of stain, dirt, blood-plaques lying upon red cells, etc.—may simulate them, but should not deceive one who looks carefully for both the blue cytoplasm and the reddish-purple chromatin. A plaque upon a red corpuscle is surrounded by a colorless zone rather than by a distinct blue body. Young estivo-autumnal parasites commonly take a "ring" form (the chromatin mass representing the jewel), which is infrequently assumed by the other varieties. The older tertian and quartan organisms show larger sky-blue bodies with more reticular chromatin, and contain brown granules of pigment, which, however, is less evident than in the living parasite. The chromatin is often scattered through the cytoplasm or apparently outside of it, and is sometimes difficult to see clearly. Typical "segmenters" present a ring of rounded segments or spores, each with a small, dot-like chromatin mass. With the tertian parasite, the segments more frequently form an irregular cluster. The pigment is collected near the center or scattered among the segments. In estivo-autumnal fever usually only the small "ring bodies" and the crescentic and ovoid gametes are seen in the blood. The gametes are easily recognized. Their length is somewhat greater than the diameter of a red corpuscle. Their chromatin is usually centrally placed, and they contain more or less coarse pigment. The remains of the red cell often form a narrow rim around them or fill the concavity of the crescent.
While the parasites are more easily found in stained preparations, the varieties are more easily differentiated in fresh blood. The chief distinguishing points are included in the following table:
| VARIETIES OF THE MALARIAL ORGANISM | ||
| TERTIAN. | QUARTAN. | ESTIVO-AUTUMNAL. |
| Asexual cycle, forty-eight hours. | Seventy-two hours. | Usually twenty-four to forty-eight hours. |
| Substance pale, transparent, comparable to hyaline tube-cast. | Highly refractive, comparable to waxy tube-cast. | Highly refractive. |
| Outline indistinct. | Distinct. | Distinct. |
| Ameboid motion active. | Sluggish. | Active. |
| Mature asexual form large; fills and often distends corpuscle. | Smaller. | Young forms, only, in peripheral blood. |
| Pigment-granules fine, brown, scattered throughout. Very active dancing motion. | Much coarser, darker in color, peripherally arranged. Motion slight. | Very few, minute, inactive. Distinctly pigmented forms seldom seen. |
| Segmenting body rarely assumes typical "daisy" form. 15 to 20 segments. | Usually typical "daisy." 6 to 12 segments. | Not seen in peripheral blood. |
| Gametes resemble asexual forms. | Same as tertian. | Appear in blood as distinctive ovoids and crescents. |
| Red corpuscles pale and swollen. | Generally darker than normal. | Dark, often bronzed. |
2. Filaria Sanguinis Hominis.—Of the several varieties of this worm, Filaria nocturna is most common and most important clinically. The adults are thread-like worms about 8 to 10 cm. long. They are rarely seen. They live in pairs in the lymphatic channels and glands, especially those of the pelvis and groin, and often occur in such numbers as to obstruct the flow of lymph. This is the most common cause of elephantiasis. Infection is very common in tropical countries, especially in Samoa, the West Indies, Central America, and the Isthmus of Panama. It is said that in Samoa 50 per cent. of the natives are infected.
The female is viviparous, and produces vast numbers of embryos, which appear in the circulating blood. These embryos are very actively motile, worm-like structures, about as wide as a red corpuscle and 0.2 to 0.4 mm. long ([Fig. 107]). They are found in the peripheral blood only at night, appearing about 8 P.M. and reaching their maximum number—which is sometimes enormous—about midnight. If the patient change his time of sleeping, they will appear during the day. Infection is carried by a variety of mosquito, which acts as intermediate host.
Diagnosis rests upon detection of embryos in the blood. They can be seen in stained preparations, but are best found in fresh unstained blood. A rather large drop is taken upon a slide, covered, and examined with a low power. The embryo can be located by the commotion which its active motion produces among the corpuscles. This motion consists almost wholly in apparently purposeless lashing and coiling movements, and continues for many hours.
3. Trypanosoma Hominis.—Various trypanosomes are common in the blood of fishes, amphibians, birds, and mammals (Fig. 81). They live in the blood-plasma and do not attack the corpuscles. In some animals they are apparently harmless; in others they are an important cause of disease.
| FIG. 81.—Trypanosomes from blood of gray rat (Boston). |