Abstract
An account is given of the incidence of the abomasal parasites in the lambs of South-West Britain. Some 600 lambs were examined, and counts of the parasites were conducted in 100 cases.It is suggested that to explain the constancy of infection with Ostertagia, and the great difference between these “healthy figures” and the pathogenic figures (10,000) of other authors, it is necessary to assume a resistance to the accumulation of the parasite present within the sheep.