Document Jr8V74DwxRvG1VvZ3xoKZ67X6

TUMORS OF THE UROGENOUS ORGANS 537 5. The religious demands for ablutions after defecation and urination entice the fellahs to drop their excreta containing the ova on the banks of canals and drains or directly into the water of them, where it is handy for the ablutions required afterward. The ova are thus placed directly into the ideal medium for further propagation of the maximum number of cercariae, as these organisms would readily die when left in a dry spot exposed to the action of the intense heat and strong actinic rays. 6. An important role in perpetuation of the disease is due the methods of cultivation of the soil, as these determine the degree and duration of its moisture. Two methods of irrigation are practised in Egypt: the ancient or basin method and the modern or canal-and-drain method. With the ancient method, the water of the Nile, which begins to rise in June, is permitted to flood the fields in August when it reaches its highest level. In October, the water is allowed to drain back into the Nile. Seeds are then simply thrown over the surface and a sort of wooden raft is passed over to smoothen the surface and to mix the seeds with the superficial soil. The farmer waits from then on for the harvest until the next April. During the early summer the intense heat dries the soil so completely that the snails, left in the former wet slush covering the ground, die. The number of infected or potential hosts for the cercariae is thus considerably diminished every year. Districts culti vated according to this system, which permits, however, only one crop a year, show a relatively low incidence of infections among the fellahs (20 per cent). The modern method of cultivation, which was introduced about 100 years ago and is spreading constantly, permits a continuous irrigation of the fields by way of irrigation canals fed from bodies of water accumulated behind dams and barrages built into the Nile. In the waters of the canals and drains, and in the vegetation of their shores, the snails thrive and thus furnish necessary and ample hosts for the cercariae throughout the entire year. The incidence of schistosomiasis among the farming population (men, women and children engaged in agricultural work) is very high (85 per cent) for this reason. While permitting the harvesting of several crops per year and thereby aiding the material prosperity of the country at large, this system has under mined the health of the farmers, as it has not only favored the spread of schistosomiasis, but also the dissemination of ankylostomiasis, dysentery and malaria (Scott). IV. INCIDENCE The incidence of vesical bilharziosis among the Egyptians is generally high, but varies in degree in different parts of the country depending upon geologi cal formation and the agricultural methods used. The disease is more common in Lower Egypt than in Upper Egypt. It affects mainly the rural population, and especially those engaged in farming. It has been stated that about 70 to 90 per cent of the population of Egypt is infected with Schistosoma, that