Page:Tropical Diseases.djvu/863

XLIV] Life-history.—Little until lately was known of the life-history of P. armillatus; it is similar to that of the European linguatulid (Linguatula tœnoides), which is also an occasional parasite of man. The ova, disseminated by snakes harbouring the adult form, reach the intermediary host probably with its food or drinking-water.* The larvæ then penetrate the mucosa, where some remain (Fülleborn); others pass on and become encysted in almost any organ or tissue, more especially liver, mesentery, or lungs. At a certain stage of development they escape from their cysts and migrate to the serous cavities, where they cause considerable inflammation. As a rule at this stage they are swallowed by their definitive host. Pathogenesis.—There is much uncertainty as to the pathogeny of this parasite. Some consider it quite harmless. There can be no doubt as to the gravity of a heavy infection at the time when the parasites are migrating in their intermediary host. In Kearney's case, reported by Aitken, twenty or thirty parasites were found encysted in the liver and one or two in the lungs. The lungs were greatly congested. In Marchoux and Clouard's case the parasites were found in the liver and in the mesentery all along the intestine, but especially about the cæcum. In Chalmers' case numerous parasites were found moving freely in the abdominal cavity over the surface of the various organs. A large number were found within the lumen of the small intestine. Many were still encysted in the lungs. The diagnosis of porocephalus infection is impossible.

This is a common parasite of the rat in many parts of the world. Christopherson found one specimen in the intestine of a Soudanese. It is a white parasite with attenuated extremities, with many rings, resembling a porocephalus. The male is 4-5 cm., the female 7-10 cm. in length.