Page:Tropical Diseases.djvu/877

XLV] and trachea pass into the œsophagus, and so to the stomach. It has been conjectured that during this passage the larva acquires the power of resisting the action of the gastric juice. If this be so, then the indirect route described must be the only way by which the ankylostome can arrive at maturity. The success of feeding experiments, which hitherto has been regarded as proof that the parasite passed directly to the stomach, may be attributed to the passage of the larvae into the wall of the œsophagus while the dose of larva-laden material was being swallowed.

Sambon has suggested that a proportion of the ankylostomum larvae pass directly, via the blood-stream, from skin to intestine. To test this suggestion, Fülleborn and Schilling-Torgau in one set of dogs divided the œsophagus, stitching the lower divided end to the skin; in another set of dogs a cannula was inserted into the trachea so that the bronchial secretion could not pass into the œœsophagus. The dogs were then infected with A. caninum. After a time both sets of dogs gave evidence of small-intestine infections of ankylostomes. Sambon's suggestion, therefore, is to some extent well founded. The duration of the life of A. duodenale in the intestine has not been determined; some state it in months, others in years (Sonsino)— one to three. On account of liability to re-infection, this point, an important one as affecting prognosis, is difficult to determine. Giles holds that A. duodenale may become sexually mature while outside the human body and in the free state; in other words, that it is heterogenetic, an abundant supply of food favouring non-parasitic multiplication. His observations, while supported by Ozzard, Annett, Ross, and Sandwith, are opposed by Looss, who points out that probably other free-living nematodes have been mistaken for the species in question; that in fact the illustrations in Giles's report represent three males belonging to different species and characterized by an entirely different configuration of the posterior extremity.