cocci (Rogers, lW), Laetobaciuus cas& (Chattaway, lW), and Laclobaeiuus bulgcrricus, strain 09 (Wieland et d., 1950; Huff et d., 1950). Further studiea with L. bulgaricw, strain 09 have revealed that ureidosuccinic acid partially replacea that orotic acid ia also a nucleic acid pyrimidine a growth factor for one of the group C streptoprecursor in mammdim tissues. Studiea of orotic acid synthwia...

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B-vitamin assays with chicks. 2 89 Roberts, E. C. & Snell, E. E. (1946). J. bid. Chem. 163, 499. Rosen, F., Huff, J. W. & Perlzweig, W. A. (1946). J. bid. Chem. 163, 343. Snell, E. E. & Rannefeld, A. N. (1945). J. bid. Chem. 157, 475. Sreenivasan, A., Harper, A. E. & Elvehjem, C. A. (1949). J. bid. Chem. 177, 117. Stokstad, E. L. R., Jukes, T. H., Pierce, J. . Page, A. C. & Franklin, A. L. (194...

In their letter to EHP, Huff et al. (1) maintained that arsenic is still viewed as "a paradoxical carcinogen; that is, carcinogenic to humans but not to laboratory animals," and that this paradox will be believed until car-cinogenicity of arsenic is demonstrated in animal experiments such as "long-term inhalation studies using arsenic trioxide." Huff et al. (1) seem not to take into considerati...

Woodward and Goodstein (1) discussed the handling of data that do not support a given hypothesis. They illustrated their point as follows: an investigator might inductively infer, after observing a large number of black ravens, that all ravens are black. According to the inductive approach, good scientific practice consists in recording all that one observes and not just some selected part of i...

ACKNOWLEOOMENTS I wish to express my special gratitude to Professor Patrick Suppes, who formulated the problems I worked on, and whose advice, guidance and encouragement at all stages of this work was invaluable. I also want to thank the other members of the reading committee, Professor ~oravcsik and Professor Hintikka, whose criticisms and suggestions were extremely useful, George Huff, who ma...