The significance of vital reaction was immunochemically observed on the sensitization of rabbit by the heterogeneous organic (canine stomach and duodenum) antigen. And the results were as follows. 1. On the sensitization of rabbit by the extracted antigen of canine stomach and duodenum with physiological salt solution, the body weight of rabbit showed a little decrease at the 1-2 week, but it gradually increased or it did not show remarkable change after then. In the blood picture, the erythrocyte count and hemoglobin value showed a little decrease around the 2-5th week after the sensitization, but the leukocyte count increased since the 1-2nd week after the sensitization and it repeatedly decreased after the 5-6th week and returned to the ...