During this time it moults twice. After the second moulting it passes into a torpid condition, in which it ceases to eat, and its growth is suspended. In this state it may live for weeks or months, moving about more or less languidly in muddy water, in mud, or in damp earth. Should chance so determine, it is finally transferred to the human alimentary canal, either in muddy drinking-water, or in the mud or dirt adhering to the hands or the food dishes of the agriculturist, the brick-maker, or other operative engaged in handling the soil; or, it may be, in earth deliberately eaten by the geophagist and children. Arrived in its final host, after moulting again at the end of five weeks (Leichtenstern), it acquires sexual characters and the permanent adult form.
Fig. 178.—A. duodenale. (After Looss.)
a, Bursa; b, head.
Until recently this was believed to be the only method of infection, but Looss has shown that the parasite may reach the intestinal canal by another route. In making some experiments with "cultures" of ankylostomum larvæ, Looss inadvertently allowed the culture to come into contact with his hand. This was followed by redness and irritation of the skin of the part and, subsequently, by well-marked ankylostomiasis; the sequence of events suggesting that the larvæ in the cultures had penetrated the skin of his hand and so attained the bowel. On another occasion Looss repeated this experiment on a human leg, an hour before its amputation. Sections of the skin showed the larvæ in the hair-follicles, and some had traversed the hair papillæ and lay in the connective tissue around the follicles.
