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Intestinal Worms

body, female, embryos, tail, canal, escape and length

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INTESTINAL WORMS.

the many varieties of parasitic worms which infest the alimentary canal in childhood, three only are of special practical importance from giving rise to disturbance or distress. These are :—The small thread-worm, the long round-worm and the tape-worm. There is one other, the large thread-worm (tricocephalus dispar), which is also occasionally met with ; but the creature seems to give rise to no symptoms, and is only discovered by its presence in the stools.

Description.—The small thread-worm (oxyuris vermicularis), often called seat-worm, belongs to the order nematoda. To the naked eye, these worms haVe the appearance of fine white threads. Both female and male speci mens exist together, the former being the larger. In both sexes the an terior part of the body is of fusiform shape. It is narrowed towards the head, which is abruptly truncated and provided with three tubercles. The male is one-sixth of an inch in length. Its intestinal tube extends the whole length of its body, and terminates in the anus at about the middle of the tail. The tail is arranged in a spiral form. The penis is minute and book-shaped. The female measures nearly half an inch in length. Its body ends in a long tapering tail, which is three-pointed at the end. Under the microscope its uterine ducts can be seen to contain a multitude of ova. The eggs are long and unsymmetrical. They may be readily hatched by exposing them to the sun in a moistened paper envelope, as in the experiments of Vix and Leuckart. When this is done, tadpole-shaped embryos escape at the end of five or six hours, and rapidly develope into slender worms. It appears from the researches of Leuekart and Heller that the embryos can escape from the ova in the human body. Hel ler states that their liberation takes place in the stomach under the influence of the gastric juice. From the stomach the creatures pass into the duodenum and upper bowel, growing rapidly as they descend the ali mentary canal ; and by the time they reach the caecum have arrived at, sexual maturity.

According to Dr. Cobbold, the caecum is the customary habitat of these parasites ; but they have a tendency to migrate, especially into the sigmoid flexure and lower rectum, and can often be seen moving about in the folds of the anus.

The long round-worm (ascaris lumbricoides), often called lumbricus, is a large nematode worm of a yellowish red Colour. The female is fifteen inches, and the male ten inches in length. The body is cylindrical, taper ing to either extremity, but more rapidly towards the head. The mouth is. triangular, having three lips. It is armed with numerous (about two hun dred) microscopic teeth. The alimentary canal is simple, without division, between stomach and intestine. The tail is conical and pointed. In the. male it is curved like a hook towards the ventral aspect of the body ; in the female it is straight. The eggs, which are excessively numerous in each female specimen, are oval in shape, and have a thick, firm, elastic, brownish shell, which is usually nodulated on the surface. In these ova, the embryos develope very slowly, for Davaine kept some alive for five years without perceiving any attempt of the immature tenants to escape from the shell. These embryos have a curious tenacity of life, for they cannot be destroyed by frost or complete desiccation. It has been doubted whether the eggs can be hatched, and the embryos escape and pass through their develop mental stages to maturity, in the alimentary canal of the subject infested with them. It appears, however, from the researches of Heller that this is possible.

The lumbricus inhabits the smaller bowel, but is migratory in its habits, and has a peculiar tendency to wander. The worms have been consequently found after death in very curious places. They have been seen in the nasal passages ; in the larynx and bronchi ; in the ducts of the liver and pancreas ; in the gall-bladder, and even in the cavity of the peritoneum, and in the interior of abscesses communicating with the abdomen. The worm has no power of penetrating the living tissues, but can pass through an ulcerated surface. Thus, it has been known to pass through an ulcerating lesion of the vermiform appendix, and set up peritonitis by entering the cavity of the abdomen.

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