The facts in the indirect method were deter mined by Looss in Egypt for the Old World type and by Claude A. Smith for the New World species in this country. When the larva are .brought on to the skin in masses of mud and water they essay at once to into the tissue. Penetrating the opening of a sweat gland or a hair follicle they reach the more open inner layers where they enter the lymph spaces and are ultimately carried into the blood stream. Borne by it into the lungs they desert the vessels to enter the air spaces. Here one finds them in the surface mucus, moving out ward. They ultimately ascend the trachea to the pharynx and pass over into the esophagus down which they travel to the stomach and intestine, thus completing their migrations. In the course of their wanderings they undergo two molts during which the structures of the adult are gradually acquired. In the intestine sexual maturity is attained in a short time and the production of eggs completes the cycle.
The hookworm attacks the surface of the intestinal wall, rasping and sucking away the delicate inner cells on 'which in fact — not on blood — the animal feed", and laying bare the deeper layers (Fig. .8). To the effects of this severe mechanical injury is added another in fluence of serious import: the worm produces in large salivary or cervical glands (Fig. 1, c)
a secretion of marked hemolytic power which inhibits the coagulation of the blood. As a result the wound continues to bleed for a long time, even after the worm has deserted the spot to which it was attached.
It is evident that environmental conditions play a large part in determining the frequence of the parasite since they favor or hinder its development in the free stage and the coincident infection of Since the eggs are killed by a temperature of 34° F. in 24 to 48 hours the paraiite never becomes abundant north or south of the subtropical tones. The encysted larva will live readily a month or even a year in moist soils but perish rapidly when the earth dries out; consequently moist climates and water-filled soils favor the spread of the parasite whereas dry seasons or absorbent soils bring about its rapid elimination whenever it chances to be introduced. For further data con sult Looss, A., 'Records of the Egyptian Gov ermnent School of Medicine> (Vols. III, IV; 1905, 1911) ; Smith, Claude A. (in Journal of the American Medical Association, Vols. XLI, XLIII; 1903, 1904) ; Stiles, C. W., Hygienic Laboratory (Washington, D. C., Bulletin 10, 1903).