“…These re sults, therefore, are in agreement with several reports in the literature [5,7,8,9,10] but disagree with the conclusions of Jakobowicz et al [6], who stated that 'both before and after the injection of tetanus toxoid the mean anti-A titers were significantly lower in type-O sons of A mothers than in O sons of O mothers at the p=0.05 level'. Their data, however, contain also information which contradicts the existence of immunologic tolerance.…”