Observations on antigenic variation in a strain ofTrypanosoma bruceigrowing in mice

Variation in agglutinating and protective antigens was studied in a strain of Trypanosoma brucei growing in mice protected with anti-trypanosomal rabbit serum. It was concluded that the agglutinating and protective antigens were the same, and that variation in the antigenic structure of trypanosome populations exposed to antiserum was due to mutation and selection rather than to adaptation. The mutation rate per organism per division cycle required to account for the experimental findings on the mutational hypothesis was found to have a mean value of 10 −5.17 .