Fig. 348.—Oxyuris vermicularis: egg twelve hours after deposition, with nematode-like embryo. × 640.
The opportunity for this is afforded every evening, as naturally the troublesome itching caused by the wandering of the worms is met by scratching and rubbing with the fingers. It is therefore possible that the eggs may even thus be introduced into the nose, where the young Oxyuris are perhaps hatched out, if they get high enough up on the moist pituitary mucous membrane. As a matter of fact, the larvæ of Oxyuris have been found in the nose. Moreover, one can understand that the eggs of Oxyuris are transferred from person to person by the hand, directly or indirectly. This again explains the wholesale infections which occur in collective dwellings, after a person harbouring Oxyuris has been admitted into boarding-houses, etc. The primary infection may be also caused in other ways—by foods, fruits, vegetables and other articles that are eaten raw, and are polluted with the ova. Perhaps also flies or their excrement play a part in the distribution of the parasite, similar to that demonstrated by Grassi as taking place in the spread of the ova of Trichocephalus and Tænia.
The assumption of a direct development without an intermediary host was first substantiated by Leuckart by experiments on himself and three of his students; about fourteen days after swallowing the eggs the Oxyuris has attained 6 to 7 mm. in length; Grassi, and later on Calandruccio, infected themselves by swallowing adult female Oxyuris, with the same results. Heller found worms in the gut (appendix vermiformis) of a male child five weeks old.
Other species are: O. compar in the cat; O. curvula and O. mastigodes in horse, ass, mule; O. ambigua in the rabbit; O. poculum in the horse; O. tenuicauda in the horse. Many species occur in insects, especially in Blattidæ and Hydrophilidæ (aquatic beetles).
Family. Mermithidæ.
Genus. Mermis, Dujardin, 1845.
With characters of the family.
Mermis hominis oris, Leidy, 1850.
Fourteen centimetres in length, 0·16 mm. in breadth; mouth terminal; posterior extremity obtuse and provided with a recurved hook 50 µ long.
The parasite was “obtained from the mouth of a child.” Stiles considers it to be probably a Mermis, possibly swallowed in an apple.