Cecil, R. L., & Steffen, G. I. (1921). STUDIES ON PNEUMOCOCCUS IMMUNITY: I. ACTIVE IMMUNIZATION OF MONKEYS AGAINST PNEUMOCOCCUS TYPE I PNEUMONIA WITH PNEUMOCOCCUS TYPE I VACCINE. The Rockefeller University Press.

Cecil, Russell L., و Gustav I. Steffen. STUDIES ON PNEUMOCOCCUS IMMUNITY: I. ACTIVE IMMUNIZATION OF MONKEYS AGAINST PNEUMOCOCCUS TYPE I PNEUMONIA WITH PNEUMOCOCCUS TYPE I VACCINE. The Rockefeller University Press, 1921.

Cecil, Russell L., و Gustav I. Steffen. STUDIES ON PNEUMOCOCCUS IMMUNITY: I. ACTIVE IMMUNIZATION OF MONKEYS AGAINST PNEUMOCOCCUS TYPE I PNEUMONIA WITH PNEUMOCOCCUS TYPE I VACCINE. The Rockefeller University Press, 1921.