“…A. suum embryonated eggs are satisfactory immunizing agents, and have been used extensively to study host responses to ^ suum (Sprent and Chen, 1949;Soulsby, 1963;Taffs, 1961bTaffs, , 1963Taffs, , 1964Taffs, , 1965Taffs, , and 1968Kelley and Nayak, 1964;Crandall and Arean, 1965;andBindseil, 1969a and1970b and c. It appears that embryonated eggs induce protective responses in hosts against challenge infections because during the in fections the host is exposed to a series of immunizing antigenic stimuli such as scanatic antigens and metabolic products, consisting of molting fluids and excretory and secretory substances.…”