eggs are very characteristic, being brownish in color, covered with a thick capsule, and having at either pole a button-like projection (Fig. 117). The length of the egg is about 0.55 mm.

The parasite occupies the cecum in man, occasionally the vermiform appendix, and sometimes the small intestine. It is particularly frequent in children in Syria and Egypt. It does not, as a

FIG. 134.-Trichocephalus dispar; natural size (Heller).

rule, produce serious disturbance, but may cause intestinal or reflex nervous symptoms. Recently it has been claimed that the parasite causes considerable disturbance by abstracting blood.

FILARIA MEDINENSIS.

The Filaria or Dracunculus Medinensis is a round-worm infesting the subcutaneous tissues and the skin. The male has not been recognized with certainty, though two recent observers have found a smaller, degenerated and partly calcified form in association with the female filaria. The female sometimes reaches a length of 60 to 80 cm.; it is yellowish in color and exceedingly elastic. In general appearance it resembles a string of catgut. The body of the worm contains a highly developed uterus, which practically fills the cavity of the worm, the intestinal tube being crowded to one side. The uterus is found to contain innumerable small embryos; these escape when the parasite is ruptured.

The organism occurs very abundantly in tropical countries of the old world, notably Arabia, along the coast of the Caspian Sea, in Abyssinia, and Guinea. The parasite is sometimes called the Guinea-worm.

The parasite infests the subcutaneous tissues, particularly those of the lower extremities, and gives rise to inflammatory lesions resembling carbuncles. The method of invasion and the life-history of the organism are obscure. It has been held that the embryos develop in water of swamps, and enter directly through the skin. This view has never been proved, and recent investigations would indicate that certain crustaceans of the family Cyclops are the intermediary host and effect the transmission to man. Some authorities believe that the invasion occurs through the gastro-intestinal tract.

FILARIA SANGUINIS HOMINIS.

Several varieties of filariæ have been found in the blood and are included under this generic term. The discovery of the organism, or rather of the embryos, was made by Wucherer, in a case of hematuria.

The embryos appear in the blood, urine, the lymph, and the tissues as thread-like structures, varying in size in the different varieties. The ordinary form has a thickness of about the diameter of a red corpuscle, and is as much as 0.2 to 0.5 mm. in length. It consists of a transparent sheath, almost completely filled with the embryo, the ends, however, projecting a little beyond the organism, in a sac-like fashion (Fig. 135). The embryo is actively motile, squirming, thrashing, or curling and uncurling itself rapidly, and thus producing more or less agitation of the corpuscles or solid bodies in its vicinity.

The number of the embryos found in the blood varies greatly; in many cases a search through several cover-glass preparations may be necessary to detect a single one. Usually they are more

abundant. A feature of importance is that they occur only during the night, unless the patient reverses the usual conditions and rests during the day.

The adult worms occupy the lymphatic channels, the male and female being found together. The male is somewhat smaller than the female and is colorless. The brownish-colored female worm is about 38 mm. in length and produces embryos in great abundance. These enter the circulation and are discharged in various ways, especially in the urine. The mosquito has been found to act as the intermediary host in which the embryo reaches its fuller development.

Filariasis is particularly common in the warmer climates, but is occasionally met with in this country, especially in the Southern States. One of its most frequent forms is characterized clinically by hematochyluria. The embryos in these cases may be found in

the blood and also in the chylous urine. Pathologically no gross changes may be found, but there may be in other cases evident distention of the lymphatic channels and blood-vessels of the pelvis of the kidneys, ureters, or bladder; and the embryos may be found in the substance of the kidneys or in the walls of the blood-vessels. Another form of filariasis is elephantiasis. In these cases there is obstruction of the lymphatic vessels in consequence of the presence of the parasites, of thrombi, or of inflammatory lesions, and as a result of these conditions dilatation of the peripheral lymphatic vessels occurs. The skin may be ruptured and chylous liquid may exude. The embryos may be found in this on microscopic examination.

Varieties.-Manson has described three varieties of embryonal filaria-the original form, or Filaria nocturna; a second variety, in which the embryos are found at any time, night or day, called Filaria perstans, which he believes the cause of the sleepingdisease of Africa as well as of certain skin diseases (Craw-Craw); the adult worm is unknown. The third form is the Filaria diurna, which appears in the blood only during the day. The last is probably the embryo of Filaria loa, a form occurring in the eye, lying under the conjunctiva. It is found in Africa and tropical America. Manson believes that the mangrove fly is the intermediary host.

OTHER FORMS OF FILARIÆ.

The Filaria lentis was found in the lens in a case of cataract. The Filaria labialis was discovered in a pustule on the lip of a student in Naples; the Filaria hominis oris was found by Leidy in the mouth of a child; and Filaria restiformis was found in the urine of a patient by the same observer. The Filaria immitis is the common filaria of the dog, and has been found in man. The Filaria bronchialis was found in bronchial lymphatic glands. in a case of phthisis, and has also been found in the trachea and bronchi. The Filaria Demarquayi and F. Magalhasi are forms whose identity has not been sufficiently established. Filaria conjunctiva, F. lymphatica, and F. Romanorum-orientalis are others that have been described.

ECHINORRHYNCHUS GIGAS.

This is a large round-worm, the body being marked by distinct, transverse, parallel rings. The male may be from 7 to 10 cm. in length, the female from 31 to 50 cm. There is a retractile rostellum, with six rows of hooklets, at the anterior end, each row composed of eight spicules. The parasite occupies the small intestine of the hog, and has been found occasionally in man. The intermediate host seems to be the grub of the cockchafer and the Junebug.

Other varieties of echinorrhynchus have been described, but are not well-determined species.

EUSTRONGYLUS GIGAS.

The female of this species may reach a length of 1 m.; the male is but one-third this size. The anterior end of the worm is retracted, and the mouth surrounded by six papillæ. The posterior end is expanded, and provided with a spicule projecting from the cloaca. The color of the worm is brownish or blood-red. The parasite is found in the pelvis of the kidneys, ureters, and bladder of dogs, horses, cattle, and other animals, and rarely in man. Among its results are enlargement of the pelvis of the kidney and atrophy of the kidney-substance.

STRONGYLUS LONGEVAGINATUS.

This parasite was found in the lungs of a child. It resembles the strongylus met with in the lungs of sheep and other animals.

TREMATODES, OR FLUKE-WORMS.

The fluke-worms are usually flattened organisms, somewhat tongue-shaped and provided with powerful suckers and occasionally also with hooklets. The intestinal canal begins in the oral orifice anteriorly, but is closed at the posterior extremity. Reproduction may take place directly or by the formation of an intermediate organism which is parasitic to certain lower animals. In this stage they are actively motile, swimming about in water, and are known as the cercariæ.

DISTOMA HEPATICUM.

The Distoma hepaticum, or liver-fluke, is from 15 to 35 mm. in length and 6 to 20 mm. broad; it is pointed at either end, and an

teriorly is provided with two suckers, one at the head and one upon the ventral surface, somewhat posterior to the first (Fig. 136). The genital pore lies between the two suckers. The eggs are oval in shape, 0.14 to 0.15 mm. in length, and provided with a lid at one pole.

The adult organism occupies the biliary ducts and is a frequent parasite of sheep. It is occasionally met with in man, usually occurring in considerable numbers. It gives rise to obstruction of the biliary passages and consequent enlargement, congestion, and later degeneration of the liver. The gall-ducts above

FIG. 136-Distoma hepati cum: two-thirds the natural

size (Mosler and Peiper).

the point of obstruction have sometimes been found considerably dilated or cystic. Clinically ascites and jaundice have been found, with gastro-intestinal symptoms and distoma-eggs in the stools.

DISTOMA LANCEOLATUM.

This form is smaller than the last, 8 to 10 mm. in length and 2 to 2.5 mm. in breadth. The two suckers are far apart, and the genital pore lies between them (Fig. 137).

The eggs are 0.04 to 0.05 mm. in length and 0.03 mm. in breadth.

This form is frequently associated with the last, and occupies the biliary passages of sheep and cattle. It is occasionally met with in other animals and in man.

DISTOMA HEMATOBIUM.

FIG. 137.-Distoma lanceolatum; two-thirds the natural size (Mosler and

Peiper).

This organism occurs in sexually distinct forms; the male and female, however, occurring together. The male is 12 to 14 mm. in length and 1 mm. thick, and the posterior part is somewhat flattened and curved ventralward to form a groove, in which the female is attached (Fig. 138). The latter is 16 to 18 mm. long, and 0.13 mm. thick. The eggs are 0.12 mm. long and 0.04 mm. broad, and drawn out

FIG. 138.-Distoma hematobium, with eggs (von Jaksch).

to a point at one end.

The adult parasite occupies the portal vein and the veins of the spleen, mesentery, and the plexuses of the bladder and rectum. The eggs of the organism may be found in any of the organs, notably in the liver, in the intestinal walls, and in the mucous membranes of the urinary passages. They probably occupy the vascular system ordinarily, but cause rupture of the walls of the vessels and thus escape into the tissues.

The pathologic changes caused by this parasite are most strikingly seen in the ureters and bladder in acute cases. Hyperemic spots or small hemorrhages may be seen in the mucous membrane, and the surface is covered with blood-stained mucus containing the eggs. In cases of longer standing roughness of the mucous membranes and usually small ecchymotic elevations or outgrowths,