In this second edition of Burnet's well-known book on the production of antibodies the authors have clarified and extended the views advanced previously. They believe that the first injection of an antigen causes the modification of intracellular enzymes, so that these become adapted to the antigen. Subsequent antigen injections stimulate the replication of the adapted enzyme units formed. The circulating antibodies are considered as partial replicas of the enzyme units, devoid of enzymic activity.
The assumption of self-producing enzyme units is based chiefly on the initial logarithmic increase of the antibody titer. The logarithmic shape of the curve leads the authors to believe that “there must be something, somewhere proliferating”. They assume that the enzymes which are normally involved in the disposal of expendable body cells, become adapted to antigens which are similar to the normal substrates of the same enzymes.