than broad. The uterus is formed like that of the Tænia solium, but the lateral branches are more numerous (twenty to thirty, and often dichotomously branched) (Fig. 116). The eggs are rather more oval and larger than those of Taenia solium, but otherwise closely resemble the latter.

The larval form, or cysticercus, occurs in the ox and sometimes in the giraffe. The measles are found in the muscles, liver, lungs, and occasionally in other organs (Fig. 121).

The adult form occurs only in man, and occupies the small intestine. The presence of the worm does not seem to occasion any definite disease of the intestines, except in rare cases, when a number are found present in a coiled mass, or when one worm is similarly coiled. This may cause intestinal obstruction, and possibly in exceptional instances rupture of the bowel.

The symptoms ascribed to tape-worms are some of them doubtless reflex; but it is noteworthy that they are often absent until the patient discovers segments in the stools. (Further reference to possible pathologic results is made in the discussion of Bothriocephalus latus.) It is an exceedingly

common parasite in certain countries (Africa and the East), but is more or less commonly found in all parts of the world.

ΤΑΝΙΑ ΝΑΝΑ.

This form, sometimes called the dwarf tape-worm, in its adult state is about 2.5 cm. in length (Figs. 122 and 123). It has a rounded head, with a rostellum that may be protruded or retracted and that bears a single circle of twenty-two to twenty-seven hooklets. The mature segments of the posterior end of the worm have a yellow color. The genital pore is on the same side in all the segments. The eggs are oval in shape, whitish and transparent; they are from 47 to 48 long and 38 to 39 broad.

FIG. 122.-Tænia nana,

The intermediary host of this form is not certainly known, but is sup

about natural size (Mos- posed to be some form of insect or snail. In the

ler and Peiper).

FIG. 123-Tænia nana,

rat the larval form occurs in the intestinal walls at the base of the villi in the form of a cysti- much enlarged (Mosler

and Peiper).

ceroid, which later discharges its contained embryo into the intestine, where it matures. The same sequence may occur in man. The adult parasite alone occurs in man. The head attaches itself deeply in the mucous membrane of the bowel, and may cause considerable local disturbance. There are usually several or many worms associated; sometimes there may be several thousands.

FIG. 124. Tænia elliptica (Mosler and Peiper).

TÆNIA ELLIPTICA.

This form is identical with Tania cucumerina. It is a common parasite of dogs and cats. The length is from 15 to 30 cm. ; the head is provided with a rostellum bearing sixty hooklets ranged in four rows; the rostellum may be protruded or retracted. At the junction of the segments there is a considerable contraction of the diameter of the worm, giving the body a markedly linked character (Fig. 124). The mature segments have a reddish-brown color from the presence of the eggs. Each proglottide has a double sexual apparatus with a genital pore at each side. The intermediary host is probably the louse of the dog and occasionally the flea. The adult worm usually occurs in numbers in the intestinal tract, and in some cases seems to produce inflammatory disturbances.

TENIA FLAVOPUNCTATA.

This form (probably identical with Tania diminuta) is from 20 to 30 cm. in length; the head is elongated and verges gradually into the neck. The suckers are small, but there is neither rostellum nor hooklets. The segments are marked by a yellowish spot which represents the male genital organs.

TÆNIA MADAGASCARIENSIS.

This form is from 25 to 30 cm. in length; the head is marked by four large suckers and a rostellum bearing hooklets.

OTHER FORMS OF TÆNIA.

Besides these more or less satisfactorily described forms, a number of uncertain varieties have been reported, such as the Tania tenella, Tania Algeriana, etc.

TÆNIA ECHINOCOCCUS.

The Tania echinococcus in its adult form occurs in the intestinal tract of the dog, the larval condition occurring in man and in some of the lower animals. The mature worm is about 4 or 5 mm. in length, and consists of four segments (Fig. 125). The head, which constitutes the first, is provided with four suckers and a rostellum bearing fourteen to twenty-five hooklets in a double row. The second segment is about the breadth of the head, but somewhat shorter. The third is considerably larger; and the fourth is the largest of all, constituting about one-half or two-thirds of the entire worm. The uterus consists of a median portion with few lateral branches. The eggs are oval, from 17 to 30 in diameter, and the shell is rather thinner than in the eggs of other tape-worms.

The adult worm occurs in great numbers in the small intestine of the dog. It is also found in the wolf and fox, and occasionally in other animals.

The Echinococcus Cyst.-This term is applied to the structure in which the larval worm is embedded. Three varieties have been distinguished.

FIG. 125.-Tænia echinococcus; enlarged (Mosler and Peiper).

(a) Echinococcus Scolicipariens.-When the eggs reach the stomach of man the embryo is freed and penetrates the mucous membrane. It is carried by the blood or lymphatic stream to the liver or other organs, where it develops an echinococcus-cyst (Fig. 126).

FIG. 126.-Echinococcus-cyst of the liver (from a specimen in the Museum of the Philadelphia Hospital.)

The wall of the cyst is composed of two layers, an outer cuticular and an inner parenchymatous, granulocellular layer. The paren

chymatous layer is important as a budding or brood-membrane. After some weeks there may be seen upon its surface small buds or projections, which later become hollowed by a central excavation and form a small cyst; secondary budlets spring from the surface of this and gradually form embryonal heads or scolices (Fig. 127). When mature these are retracted or inverted into the cavity or cyst of the original bud. In this manner a large number of heads are formed upon the inner wall of the original echinococcus-cyst, the cavity of the cyst at the same time increasing in size and being distended with characteristic liquid. This is a clear fluid, having a specific gravity of from 1009 to 1015 and a neutral or alkaline reaction, and containing no albumin or only traces, but a considerable quantity of chlorid of sodium. Sugar is sometimes found in the fluid.

FIG. 127.-Formation of buds upon the parenchymatous layer (Leuckart).

(b) Echinococcus Hydatidosus.-Besides this form of simple cyst with buds attached to the inner wall, there are cases in which daughter-cysts and even granddaughtercysts are formed. The daughter-cysts are found within the original cyst, and are probably produced by cystic degeneration of the buds already described; and possibly in some cases by simple separation of the buds. They are variable in size, sometimes becoming as large as a nut or egg, and when granddaughter-cysts are contained within them the size may be even greater. To this form the term Echinococcus hydatidosus or Echinococcus endogenes is applicable.

In a subvariety of this form secondary cysts are produced outside the original wall. These are formed by a process of softening in the cuticular wall, with gradual projection of the parenchymatous layer toward the exterior and eventual rupture, with formation of secondary cysts outside.

(c) Echinococcus Multilocularis.-In a third form of echinococcus-disease there are numerous small cysts, from the size of a grape-seed to that of a pea, embedded in connective tissue, and altogether forming a more or less definite tumor-mass. On section this presents an alveolar appearance, the cysts containing somewhat gelatinous material. Careful examination of the inner walls of the small cysts shows them to contain pigment and calcareous particles. Scolices, however, are absent for the most part, the cysts being generally sterile. The term Echinococcus multilocularis is applied to this variety of disease (Fig. 128). Its formation is explained by the assumption that there are secondary proliferations in an outward direction from the original cyst, rather than a deposit of large numbers of ova or embryos. The whole mass presents the appearance of a tumor, and not rarely central necrosis and softening occur as in tumors.

Echinococcus cysts may continue to grow until they have reached huge dimensions without undergoing any secondary changes. In other cases the parasite may die and the growth may cease, or active proliferation of the tissues around the cyst may lead to early destruction. In still other cases suppurative change occurs in the cyst or its wall. In all cases when the cyst reaches a certain size the tissues around produce a connective-tissue capsule of greater or less thickness. When the parasite dies inspissation of the liquid occurs, and it may eventually disappear or be converted into a thick whitish material; the cyst-walls and the connective

FIG. 128.-Echinococcus multilocularis (Luschka).

tissue capsule at the same time shrivel and present peculiar concentric lamellations that are very characteristic. Eventually calcification of the wall of the cyst and to a certain extent of its contents takes place.

Seats.-Echinococcus cysts are most frequent in the liver. They also occur in the lungs, kidneys, spleen, and omentum, and less frequently in the brain or other parts of the nervous system. The pathologic effects are produced by direct mechanical pressure.

The geographical distribution is extensive, but the disease is common only in restricted localities, especially in northern countries (north of Europe, Iceland).

BOTHRIOCEPHALUS LATUS.

The Bothriocephalus latus is the largest tape-worm of man, reaching the length of from 5 to 9 m. The head is flattened. and club-shaped and presents two groove-like suckers at its sides (Fig. 129). The neck is thin and gradually increases in diameter. The ripe segments are quadrate, and are distinguished by a rosettelike formation of the uterus, which is plainly visible in the center of each proglottid (Fig. 116). The genital pore is upon the flat surface of the segment and always upon the same side of the worm. The eggs are oval in shape and enclosed in a shell presenting a hinged lid at one pole. The intermediary host is some form of fish, most frequently the pike. The eggs first undergo a