Abstract
A detailed study has been made of an antibody which appears in the blood of certain rabbits implanted with the Brown-Pearce carcinoma or injected with extracts of it and which reacts specifically in vitro in mixture with a distinctive sedimentable constituent of the Brown-Pearce tumor cell. The observations as a whole seem to indicate that this constituent of the Brown-Pearce tumor differs notably from certain other sedimentable substances which can be extracted from various rabbit tissues and identified by serological means. The implications of the findings are discussed.