Immunity conditions in young animals have long been investigated very extensively. Most of these studies have been concerned with the transmission of antibodies from the mother to the offspring with the blood through the placenta and by the milk. Comparatively little work has been done on the subject of antibody-formation in young animals. Yet it is obvious that antibody-formation in young animals is an important factor in their resistance to certain infectious diseases, in their behaviour in the phenomenon of hypersensitiveness, and in their capacity to be actively immunized with toxinantitoxin mixtures, anatoxin and vaccines. A few experiments have been reported indicating that antibody-formation varies with age in vaccinated infants and children. According to Frankenstein (1) only 3 of 30 infants produced agglutinins after vaccination with typhoid vaccine. Halber, Hirszfeld and Mayzner (2) in their careful work demonstrated that after vaccination against typhoid the agglutinin titer of the serum is moderately but decidedly lower in infants than in children from two to five years of age.