COMPARATIVE STUDIES ON BACTERIAL CYTOCHROMES**These researches have been made possible by the continued financial support of the C. F. Kettering Foundation. Much of the work was done at the Hopkins Marine Station, Pacific Grove, California, the facilities of which were most kindly placed at our disposal by Professor C. B. VAN NIEL and Professor L. R. BLINKS. Electrophoretic and centrifugal equipment needed for some of the purification procedures was made available by Dr. H. SCHACHMAN, Department of Biochemistry, University of California, Berkeley, California, who also was most generous in donating valuable time for helpful discussions. The technical assistance of Miss JEAN MILLER in Dr. SCHACHMAN'S laboratory is also gratefully acknowledged.