The diagnosis is made by detection of the worms or ova in the feces. The latter are generally numerous. They are elliptic, measuring about 50 by 70 µ, and have an unsegmented protoplasm (Fig. 105). The shell is thick, and is surrounded by an uneven gelatinous envelop which is often stained with bile.

FIG. 105.—Eggs of Ascaris lumbricoides
(Mosler and Peiper).

(2) Oxyuris Vermicularis.—This is the "thread-worm" or "pin-worm" which inhabits the colon and rectum, especially of young children. Its presence should be suspected in all unexplained cases of pruritus ani. The female is about 1 cm. long; the male, about 0.6 cm. (Fig. 106).

FIG. 106.—Oxyuris vermicularis and egg: a, Natural size; b, egg (after Heller).

The worms are not infrequently found in the feces; the ova, rarely. The latter are best found by scraping the skin at the margins of the anus, where they are deposited by the female. They are asymmetrically oval, about 50 µ in length, and often contain a partially developed embryo.

(3) Filaria Sanguinis Hominis.—A description of this worm will be found in the chapter upon the Blood, [p. 194]. The embryos are sometimes found in urine and chylous fluids from the serous cavities. Their motion is then usually less active than when in blood. That shown in Fig. 107 was alive sixty hours after removal of the fluid. Embryos were present in the blood of the same patient.

FIG. 107.—Filaria sanguinis hominis (embryo) in chylous hydrocele fluid; length, 300 µ; width, 8 µ. A number of red blood-corpuscles also appear (studied through courtesy of Dr. S. D. Van Meter).
FIG. 108.—Trichinella spiralis (larvæ) from head of right gastrocnemius muscle; seventh week of disease (two-thirds objective; eye-piece 4) (Boston).

(4) Trichina (Trichinella) Spiralis.—This is a very small worm, not exceeding 3 mm. in length when fully developed. Infection in man occurs from ingestion of insufficiently cooked pork, which contains encysted embryos. These reach maturity in the small intestine. The female produces great numbers of young, which migrate to the voluntary muscles, chiefly near the tendinous extremities, and there become encysted.