For over a quarter of a century students interested in immunological studies on the larger animal parasites devoted their attention to various immunological and serological tests that could be used in diagnosis or that could be used in elucidating systematic and immunological relationships. As you know, these studies have yielded many interesting facts and have resulted in the perfection of delicate immunological tests as, for example, those used in hydatid disease. During the first part of this period, few studies were undertaken on the prevention or termination of infection by acquired immunity, but about ten years ago investigators began to demonstrate that previous infection with certain metazoan parasites or immunization with dead vaccines prepared from them resulted in a greater or less acquired immunity to reinfection or superinfection (1). In discussing the mechanism of these acquired immunities, I shall mention only briefly some of the studies on the actual demonstration of acquired immunity and shall have to omit the general immunological and serological studies.
Fourth Charles Franklin Craig Lecture delivered before the Thirty-fifth Annual Meeting of the American Society of Tropical Medicine, November 21, 1939, at Memphis, Tenn.