In the case of parasitic infestations with protozoa and helminths, chemotherapy has not been entirely effective since the host is generally sensitive to the same agents as the parasite. Elimination of intermediate host populations, such as the mosquitoes which harbor malarial parasites, is extremely difficult in practice and can be undertaken only when the intermediate host species is economically and ecologically unimportant. The introduction of meat inspection and general education of the public as to sanitation and proper food preparation have done much to curb man's parasite-related miseries. Water purification, avoidance of fecally contaminated water, abandonment of the use of "nightsoil" as a fertilizer in agriculture, and certain food pretreatments such as salting and freezing, have also helped to alleviate the spread of parasites. Nevertheless, parasitism of humans and livestock persists in some degree in all parts of the world, despite the measures already taken to control it. There is need to explore and develop other methods of controlling parasites.