Abstract
1. Measurements have been made on the glucose and amino acid concentrations, temperature and pH in the lumen of the small intestine of the domestic duck in the region inhabited by the acanthocephalan parasite, Polymorphus minutus. 2. The glucose concentration was found to vary from 23 mg./ml. to no detectable glucose, with an average value of about 5.7 mg./ml. for the twenty-four ducks examined. 3. Sixteen amino acids were detected by qualitative and quantitative methods. 4. The temperature in the parasite's habitat is the same as the other published deep body temperatures of domestic ducks. The pH appears to be about 7.5.