. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. Fig. 104. Eggs of hookworms in early stages of segmentation, — four-segmented type most common in faeces; A, Necator americanus; B, Ancylostoma duodenale. the host, usually in a continuous stream, but occasionally with intermissions, to be passed with the faeces. The thin-shelled eggs, which are about 60 ^ by 35 ai {-^is by 7^^ of an inch) in size, and slightly larger in the American species, undergo the first stages of development while still in the intestinal canal, and by the time they are voided wit
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. Fig. 104. Eggs of hookworms in early stages of segmentation, — four-segmented type most common in faeces; A, Necator americanus; B, Ancylostoma duodenale. the host, usually in a continuous stream, but occasionally with intermissions, to be passed with the faeces. The thin-shelled eggs, which are about 60 ^ by 35 ai {-^is by 7^^ of an inch) in size, and slightly larger in the American species, undergo the first stages of development while still in the intestinal canal, and by the time they are voided with the faeces they are segmented into from two to eight cells (Fig. 104). The segmented condition, together with the fact that they are clear and not yellow or brown from bile stain, distin- guishes the eggs from those of many other worms found in the intestine. Further development does not take place until the faeces are exposed to air, when, if moisture is present and the temperature is moderately high (65° to 85° F.), the development continues and the embryo hatches in from 24 to 48 hours (Fig. 103C). Below 65° F. development is very slow, and above 85° F., although development is very rapid, the eggs and larvae are likely to die. The newly hatched worm is about mm. (less than a hundredth of an inch) in length with a bottle-shaped oesophagus, a simple intestine, and practically no re- productive organs. The most favorable conditions for the devel- opment of the larvae, in addition to the temperatures mentioned, are a moderate degree of moisture, presence of air, plenty of food in the form of decomposing organic matter, and not too rapid putrefaction. According to Looss, the larvae will not develop well in faeces derived from a purely vegetable diet, a small propor- tion of animal matter being essential for food. Enough animal food for some development would always be provided by blood from intestinal hemorrhages. On the other hand a purely meat diet is unfavorable o
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