Some Relationships Between Trichostrongylid Infestation and Cobalt Status in Lambs * *—“Lambs” is used here to mean sheep in their first year. : Haemonchus Contortus Infestation † †—An abstract of this paper was presented at the First International Congress of Parasitology, Rome, 1964. Extracted from a thesis presented to Dublin University for the degree of Ph.D.