Abstract
1. The lacto-globulin in bovine colostral whey, and the γ globulin in the serum contain the normal and induced agglutinins to the protozoon Trichomonas foetus.2. A decline in γ globulin in sera from cattle approaching calving may be associated with the concentration of the lacto-globulin in the udder.3. The elimination of the passive normal and induced agglutinins acquired by the neonatal calf was logarithmic. The autogenous production of γ globulin by the calf occurred soon after birth, resulting in an apparent decline in the rate of elimination of the lacto-globulins.4. The autogenous production of γ globulin was not necessarily accompanied by that of detectable normal agglutinin.5. Calves injected with T. foetus antigen within the first 3 weeks of life, and in which there was evidence of autogenous γ globulin, developed normal autogenous but not induced agglutinins.6. Calves which received colostrum containing maternal induced and normal agglutinins, calves partially deprived of colostrum, and calves immunized in early life, produced the normal autogenous agglutinin between the 30th and 60th days, reaching the normal adult titre of 1/48–1/96.7. The properties of the normal agglutinins were investigated. They possess some characteristics significantly different from those of the induced agglutinins. These suggested that the normal agglutinins were γ globulin molecules with an ‘accidental’ genetic configuration complementary to T. foetus.The author wishes to thank Dr M. Robertson, F.R.S., and Sir Alan Drury, F.R.S. for their interest and encouragement during the course of this work, and Dr R. C. Campbell for the statistical analysis.