The lesions associated with the migration of the larvæ of Ascaris megalocephala through the tissues of the host were studied in rabbits, guinea pigs and mice. In addition to studying the changes in those organs directly invaded by the larvæ in the course of migration, an organ remote from the migratory route but exposed to the action of any toxic products elaborated by the larvæ was also examined. In each case therefore, sections were prepared from (a) liver, (b) lungs and (c) kidneys.

Preliminary studies in Lancashire and Cheshire (Smith and Prentice, 1929) have indicated that under certain conditions there is a positive association between the disease known as “potato sickness” and the intensity of root eelworm, Heterodera schachtii Schmidt, as measured by the cyst content of the soil. This association does not appear to be constant, as a moderately high cyst content may occur in the absence of obvious disease. It has also been found (Smith and Miles, 1929) that under conditions prevailing in the North West of England the cyst content of the soil increases only after a crop which is not a total failure.