certain amount of development in water, the embryo becoming free and floating about or being propelled by a ciliated outer covering and then entering the digestive tract of fish.

U

FIG. 129-Head and

neck of Bothriocephalus latus (Leuckart).

The geographical distribution is comparatively restricted. It is frequent in certain northern countries, as in Sweden, and in parte of central Europe, especially in Switzerland. It is only occasionally met with in America ir immigrants.

BOTHRIOCEPHALUS CORDATUS.

This variety is much smaller than the last, the maximum being from 1 to 1.25 μ. The head is short, broad, and heart-shaped, and the suckers are placed upon the flat surface. The uterine structure differs from that of Bothriocephalus latus in being narrower and more elongated, and also in having lateral branches. The body of the worm contains granular calcareous matter.

BOTHRIOCEPHALUS CRISTATUS.

This form is about 3 m. in length, and is distinguished by two crest-like projections upon the head. These are covered with numerous small papillæ. There are no definite suckers, and the head contains abundant granular calcareous matter.

BOTHRIOCEPHALUS LIGULOIDES.

This variety occurs only in the larval form in man. It has been found in the region of the loins and in the tissues about the eyes. The head of the worm is distinguished by a papilla-like projection.

NEMATODES, OR ROUND-WORMS.

ASCARIS LUMBRICOIDES.

The Ascaris lumbricoides, or ordinary round-worm, is one of the most frequent intestinal parasites. The male may reach a length of 25 cm. and a thickness of 2 to 4 mm.; the female is longer, up to 40 cm., and thicker, up to 5 or 6 mm. The body of the worm is brownish or sometimes pinkish in color, and presents parallel ridges or rings somewhat like those of the earthworm. The head is provided with three rounded prominences or lips, between which the mouth is placed (Fig. 130). The male shows two chitinous spicules at the cloaca. The eggs of the worm are produced in great numbers; they are covered with a tough shell, and surrounding this is a clear material in an irregular mass.

The contents of the eggs consist of a granular material, sometimes showing the linear outlines of an embryo.

The ascaris develops in man from swallowing of the eggs in infested drinking-water or food. The parasites may be present singly or in numbers. They occupy the

small intestine, but frequently migrate, entering the gall-ducts, the stomach, the esophagus, and even the larynx or nasal cavities.

Pathologic Physiology.-Ascarides may give rise to violent symptoms by obstruction of various passage-ways, and when in numbers or united in masses even intestinal obstruction may be caused. It is probable that ascarides produce irritating secretions, as it has been observed that considerable dermatitis sometimes arises in persons handling them. Occasionally abscess-cavities containing lumbricoids are found in connection with ulcerations and perforation of the intestines. These abscesses were believed by older authors to be caused by the worms; at the present time it is more generally held that the worms play no important part, their presence being due only to their coincidence in the intestine.

b

coides: A, female: B, male; C,

is much smaller than the ordinary roundworm, the male reaching a length of 45 FIG. 130.-Ascaris lumbrior 60 mm., and the female 120 or 130 egg, magnified 300 diameters The head is distinguished by two b, head, magnified (after Perls). lateral wing-like projections composed of chitinous material.

mm.

ASCARIS MARATIMA.

This form has been observed but once, and the female alone was found.

OXYURIS VERMICULARIS.

The oxyuris, seat-worm, or pin-worm, is one of the commonest parasites of man. The male is 2.5 to 5 mm. in length; the female, 10 to 12 mm. (Fig. 131). The posterior end of the male is blunt and curved upon itself; in the female it is elongated. The eggs of the oxyuris, which are produced in great numbers, are oval or

elliptical and about 5 long. The embryo is visible within as a lobulated body. The parasite is developed directly from the eggs. When these are swallowed the outer coating is dissolved in the stomach and the embryos escape, to reach their full development in the small intestine. The impregnation occurs in the small intestine and within a short time after the swallowing of the eggs. After impregnation and ripening the female parasites move toward the rectum and may be discharged, or may leave by their own movements. The life of the worm is short, but there is always the possibility of reinfection.

a

b

FIG. 131.-Oxyuris vermicularis: a, female, b, male (Mosler and Peiper).

Oxyuris is especially common in childhood. It is probable that the worms sometimes cause inflammatory troubles. In cases in which they accumulate in numbers a form of verminous diarrhea may be produced. In female children vaginitis frequently results from the migration

of the parasites into the vagina.

TRICHINA SPIRALIS.

The Trichina spiralis occurs in its larval form in the muscles or organs of man and in the lower animals; in the adult form it is found in the intestines of man or animals.

The adult male is about 1.5 mm. in length and 0.14 mm. in thickness. At the posterior end there is a retractile cloaca flanked by two projections. The female is 2 to 4 mm. in length and 0.6 mm. in thickness. The eggs are provided with a very thin shell, and the embryos escape from this within the uterus. They are produced in immense numbers. The young embryos found in the intestinal tract are from 0.1 to 0.16 mm. in length, the anterior end thicker than the posterior. In part they escape with the

a

FIG. 132. Trichina-capsule with its connective-tissue covering: a, early stage; b, calcified (Leuckart).

feces, and die; the greater part penetrate the intestinal wall and are carried to various parts of the system, embedding themselves especially in the muscles, where they undergo further changes. Here the organism coils itself and becomes surrounded with a capsule, which is at first transparent, but may subsequently undergo calcareous change and become opaque (Fig. 132).

Trichinæ are acquired by man by eating improperly cooked ham. The

capsules are digested and the larval trichinæ set free. In the

small intestine they reach their maturity in about three days; the females are impregnated, and some days later discharge the embryos, some of which die or escape with the feces, while others probably bore their way into the mucous membrane. Many of the females penetrate the intestinal walls, and especially the lymphatic tissues of the walls, where they liberate their embryos. These are disseminated throughout the body by their own migrations or with the lymph- and blood-streams.

The favorite seat is the striated muscle-tissue, and they lie within the muscle-bundles themselves or less frequently between them. They reach their destination in ten days after the primary invasion, but subsequent crops are deposited as the young continue to mature in the intestines. In two or three weeks they begin to become encysted in the muscles.

When the embryos are liberated in the stomach and intestines they occasion violent gastro-intestinal irritation, with vomiting, diarrhea, and often more or less pronounced collapse. In their later migration the worms set up intense muscular pains of rheumatoid character, with edematous swelling and fever.

Trichiniasis is common in all parts of the world, but has been largely reduced by greater care in the cooking of pork.

ANKYLOSTOMA DUODENALE.

The Ankylostoma duodenale, or Dochmius duodenalis, is a cylindrical worm, the female being from 7 to 16.5 mm. in length; the male, from 7 to 11.2 mm. The head is rounded, and is armed

FIG. 133-Anchylostoma duodenale: a, male, natural size; b, female, natural size: c, male magnified; d, female magnified; e, head, greatly magnified; f, eggs (von Jaksch).

with six sharp, hook-like teeth. The female is usually of a brownish or reddish color, due to absorption of coloring-matter of the blood. The eggs are easily distinguished, being elliptical-shaped,

from 0.056 to 0.063 mm. in length and 0.036 to 0.04 mm. in thickness. The shell is separated from the contents, and the latter have a granular appearance, are brownish, and in the state of segmentation. The eggs may appear in the stools in great numbers. The embryo is fully developed outside the body, and entering the stomach and intestines of man there undergoes full develop ment (Fig. 133).

The adult worm occupies the small intestine. It may be present in small or large numbers, and is usually rather firmly attached to the mucous membrane. Changes in the latter, however, are not pronounced.

Patients harboring this parasite frequently become intensely anemic. It was this parasite which was found in many cases of Egyptian chlorosis, and it is the same organism that produced the intense anemias (pernicious anemia) of the laborers engaged in building the St. Gotthard tunnel.

ANGUILLULA INTESTINALIS AND STERCORALIS.

The Anguillula intestinalis occupies the intestinal tract and the ducts communicating with it. It is an actively motile, cylindrical organism about 2 mm. in length. Only a female form exists; this by parthenogenesis producing eggs from which male and female embryos are developed. The latter in their adult form differ from the original worm and were regarded as a different organism-Anguillula stercoralis. These are never found in fresh feces, and in autopsies only when this has been delayed some time after death. The male is somewhat smaller than the female. In the latter the posterior extremity is drawn out to a fine point and straight; in the former it is thicker and curled upon itself. Besides this distinction the male bears two spicules projecting from the cloaca. The embryos formed by the Anguillula stercoralis develop into the original form, the female Anguillula stercoralis. Besides this method of indirect reproduction through the stage of A. stercoralis, direct formation of A. intestinalis may occur.

These organisms have been found with special frequency in Cochin China and other eastern countries, occurring in the intestinal tract in cases of severe diarrhea. It is doubtful whether they have definite pathologic significance.

TRICHOCEPHALUS DISPAR.

The anterior portion of this parasite is thin and thread-like, while the posterior portion is thicker. The length of the worm is from 4 to 5 cm., the male being somewhat the smaller. The thicker part of the male is curled upon itself and blunt at the end, while that of the female is straight and more pointed. The