Acquired Immunity to Ticks

It is well known that the American dog tick, Dermacentor variabilis Say, can be reared through its entire life cycle on guinea pigs. In the course of permitting successive batches of larvae of this tick to engorge on the same guinea pig, it was repeatedly observed that, while the first batch always gave a large number of engorged larvae, the following batches gave few or none. This suggested that guinea pigs, after one infestation with larvae of D. variabilis, acquire an effective immunity against these ectoparasites. The experiments reported in this paper show that such an immunity is indeed developed, and that it may be solid enough to prevent larvae from engorging and to reduce the amount of blood taken by nymphs and adults.