A decline in parasitemia in herring gull chicks, noted just before fledging, was thought to have been due to an immunity to the parasites being developed by the birds. Since few investigations of the blood of wild birds had been done, a study of the blood of the gull was made to try to correlate changes in the blood with the decline in parasitemia. The serum protein levels were determined electrophoretically in birds infected with Cyathostoma lari and in uninfected birds, and leucocyte counts in infected and uninfected birds were compared.

The albumin levels in the serums of the birds decreased with age, and a corresponding increase in the globulin level was observed. The serum globulin level also increased in birds inoculated once with C. lari. No changes in the globulin level in the serum of a bird infected 3 times with C. lari were observed. Counts of various types of cells in the blood of infected and uninfected herring gulls indicated that heterophilia and eosinophilia occurred approximately 3 weeks after inoculation. The changes in serum constituents and blood cell counts of domestic fowls were compared with those of the herring gull. The results suggested that a definite cellular and immune response developed in herring gulls infected with C. lari.

Muskrats (Ondatra zibethicus) collected from three different habitats: river, marshes and streams were examined for helminth parasites. Muskrats were aged by a lens-weight technique. Using the age specific prevalence, transmission rats for Wardius zibethicus, Quinque-serialis quinqueserialis, Echinostomum revolutum and the strobilo-cercus stage of Hydatigera taeniaeformis were constructed for stream muskrats. Parasite burdens and the occurrence of multiple infections increased with host age. Differences in prevalence between habitats were observed.