This study was undertaken to determine whether the suspected periodontopathogens Bacteroides melaninogenicus ss melaninogenicus and intermedius and Bacteroides asaccharolyticus are killed by clinically used topical fluorides. The viability of each organism was examined after exposure to three fluoride compounds, stannous (SnF2), acidulated phosphate (APF), and neutral sodium (NaF), for 1 and 8 h. Stannous fluoride was found to be effective at lowest fluoride concentrations with APF next in effectiveness. NaF required the highest concentrations of fluoride to kill test organisms. Longer exposure times were found to be more effective at lower concentrations. Data obtained in this study with gram-negative organisms support and extend previous information regarding the antibacterial effect of fluorides against gram-positive periodontopathogens.

The effect of three commercially prepared fluoride compounds (acidulated phosphate fluoride 1.23% F-, stannous fluoride 0.4%, and sodium fluoride 0.05%) diluted to various concentrations with brain heart infusion broth, on the growth of five strains of Actinomyces viscosus following 1 and 24 hours' exposure to the fluorides was studied. Results demonstrated that SnF2 was the most effective growth inhibitor of the organisms at 500 ppm F- after 1 hour and at 100 ppm F- after 24 hours' exposure. APF and NaF were not effective within a 1 hour exposure period, but did suppress growth of the organisms at 200 ppm in the cultures exposed for 24 hours.

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Square planar bis(diethy1dithiophosphato)nickel(I1) forms a stable, paramagnetic, 1:l adduct with triphenylphosphine which in solution undergoes rapid triphenylphosphine exchange.ALTHOUGH a variety of bases are known to form both 1 : l and 2:l adducts in solution with square planar bis(dialky1 dithiophosphato)nickel(II), only 2 : 1 six co-ordinate adducts have been isolated and characterized. 1-4 The six co-ordinate adducts have been the subject of a number of recent spectroscopic investigations. 1 We report that triphenylphosphine reacts readily with Ni(dtp),, [dtp = (EtO),PS,-] to form dark green crystals of the first example of a 1:1, five co-ordinate adduct of Ni(dtp), isolated in the solid state, K, = 1.2 f 0.3 1 mol-l, E (6000 A) = 154 f : 5.All attempts to prepare the 2:l adduct failed. A spectral analysis indicated that only a 1:l adduct is formed in solution with metal :triphenylphosphine mole ratios of up to 470:l. The ease with which the 1 : l complex could be isolated is in marked contrast with the impossibility of

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