Abstract
Repeated infections with T. crassicauda gave autopsy results suggestive of induction of an acquired resistance, but numbers of worms recovered were too few to warrant definite conclusions. Cultures of T. crassicauda eggs in sera of repeatedly infected rats showed a marked contrast to cultures of eggs in sera of parasite-free rats. Precipitates developed around numerous embryonated eggs incubated in resistant sera. No precipitates appeared around eggs in normal sera. Larvae which hatched out of eggs in serum cultures were unaffected by precipitates. A possible partial explanation of the reaction of resistant serum to eggs is suggested, but must be tested in future expts. The reaction is believed to be of antigen-antibody nature. Application of the reaction of serum vs. ova to other helminth parasites may open wide possibilities in the field of diagnosis.