The quantitative determination of chlorinated-insecticide residues in treated foodstuffs by total chlorine methods is expedited and simplified by the exploitation of an unusually sensitive direct potentiometric method for chloride ion. This method uses a pH meter and a silver-silver chloride vs. calomel electrode system, and responds reproducibly to as little as 0.02 p.p.m. of chloride ion. With the equipment and procedures recommended, the useful range, without concentration or dilution stages, appears to be from 0.02 p.p.m. to 10,000 p.p.m.

An impediment to progress in the study of the course of growth, the effects of medium components, antibiotics, etc., of Mycoplasma has been the cumbersome methods of growth measurement currently in use. Heretofore, it required the plating of numerous samples during growth, at least in triplicate, after appropriate dilution, followed by a delay of 2 to 3 days before the colonies developed so that counts could be made. We applied the technique of light scattering to measure the growth of Mycoplasma laidlawii in liquid culture continuously in a manner analogous to the use of absorbancy for bacteria. Scattered light measurements precisely paralleled data obtained by the tedious method of plate counts and were available immediately during the development of the culture. The lower limit of sensitivity with the system described is 105 Mycoplasma per ml. The presence of serum in the medium lowers sensitivity somewhat. However, concentrations of serum up to 10% are easily tolerated. Higher serum content may require calibration curves. Thus the technique may be used with many pathogens, etc., that require serum to develop. One can easily and rapidly measure differences in growth rates as well as final cell yields during the course of growth, rather than 3 days later, after colonies have developed.

Die Bestimmung der GroBe von PVC-Latexteilchen mit mittleren Teilchendurchmessern kleiner 40 nm gelingt durch Ultrazentrifugation mit schlierenoptischer Detektion. Bimodale Latices rnit Verteilungsmaxima oberhalb und unterhalb 40 nm konnen durch Ultrazentrifugation und getrennte Detektion mittels Triibungsmessung und Schlierenoptik charakterisiert werden. Ultrazentrifugation, Elektronenmikroskopie, Lichtstreuung und Trubungsmessung fuhren bei monomodalen Latices fur vergleichbare Mittelwerte zu gleichen mittleren Teilchendurchmessern. onpeaeJcenuu pacnpeaefienw uacmuy no p a m e p a 4 y nofiusunufimopudnux JcameiicosYJIbTpaqeHTPH~yrUpOB~EIeM OlIpeAeJIHJIklCb pa3MepbI IIOJIHBHHHJIXJIOPHAHMX JIaTeHCHbIX raCTEiq. Y WiCTEIq CO CPeRHHM AMaMeTpOM HHme 40 HM AeTeKTHpOBaHHe IIpOki3BOAHJIOCb mJIHPeH-OIITL19eCKHMH Ei3MePeHHRMH, a B Cnyqae 6MMOfiaJIbHbIX JKlTeKCOB C MaKCEiMYMOM PaCIlpeAeJIeHHR BbIUIe EI HEHI? 40 HM -ITIJIEIPeH-OIITH9eCKHMH COBMeCTHO C He@?JlOMeTpH9eCKElMH ElklMepeHHHMEI. YJIbTpaqeHTpkI~yrEIpOBaHEle, BJIeKTPOHHaH MMKPOCKOIIHH , CBeTOpaCCeHHHe KOBbIM CPeAHElM AMaMeTpaM naCTMq.n nemepe~k~e MYTHOCTEI IIPEBOAHT npn MoHoMoAamHMx naTeKcax B cnysae CpaBHnMMx cpenmx s n a r e~n i i K onmaDetermination of the particle size in polyvinyl chloride latices Determination of the particle size in PVC latices a t average particle diameters smaller than 40 nm is achieved by ultracentrifugation combined with strioscopic detection. Bimodal distributions having maxima above and below 40 nm can be characterized by ultracentrifugation and seperate detection by turbidimetric and strioscopic methods. Ultracentrifugation, electron microscopy, light scattering and turbidimetry provide comparable particle diameters of monomodal latices for corresponding average values.

An impediment to progress in the study of the course of growth, the effects of medium components, antibiotics, etc., of Mycoplasma has been the cumbersome methods of growth measurement currently in use. Heretofore, it required the plating of numerous samples during growth, at least in triplicate, after appropriate dilution, followed by a delay of 2 to 3 days before the colonies developed so that counts could be made. We applied the technique of light scattering to measure the growth of Mycoplasma laidlawii in liquid culture continuously in a manner analogous to the use of absorbancy for bacteria. Scattered light measurements precisely paralleled data obtained by the tedious method of plate counts and were available immediately during the development of the culture. The lower limit of sensitivity with the system described is 10 5 Mycoplasma per ml. The presence of serum in the medium lowers sensitivity somewhat. However, concentrations of serum up to 10% are easily tolerated. Higher serum content may require calibration curves. Thus the technique may be used with many pathogens, etc., that require serum to develop. One can easily and rapidly measure differences in growth rates as well as final cell yields during the course of growth, rather than 3 days later, after colonies have developed.