Abstract
The M.I .D. for mice of mature embryonated eggs was found to be about 30,000, indicating a strong natural resistance to infection with Ascaris lumbricoides suum. When mice were treated with morphine sulfate (1%) to artificially slow intestinal emptying time, they were rendered more susceptible to infection with ascaris eggs than untreated controls given the same number of eggs. The reduced intestinal emptying time presumably allows greater numbers of eggs to hatch than in control animals.