Observing bacterial activity interferometrically.

It is shown that bacterial activity, even of slowly growing species, can be detected by precise interferometric measurements of refractive index changes of the culture medium. The bacteria-containing sample is kept in an isothermal block together with a reference liquid without bacteria. The biological activity is obtained from the difference of the index changes of these samples. Experiments were performed with Bacilo Calmette-Guérin. The order of magnitude of the observed total refractive index change was compatible with theoretical estimates based on the amount of available oxygen. An unexpected positive index change during the lag phase was observed, which might permit fast diagnostics in medical applications. This technique may provide cheap and quick tests of bacterial susceptibility with respect to antibiotics.

Analysis of the resonant scattering of light by cylinders at oblique incidence.

We study the resonant scattering of light at oblique incidence by dielectric uncoated and coated cylinders. We develop a stable algorithm that permits us to calculate the resonances of a single dielectric cylinder as the tilting angle varies. This algorithm is based on semiclassical formulas for the distance between resonances. Results show that the resonances and the resonant electromagnetic energy flux near and internal to the cylindrical surface are highly sensitive to variations in the tilting angle. In addition, the coating effects are studied for scattering of light at oblique incidence by an infinite, perfect cylindrical conductor coated by a dielectric layer. In this case the resonance calculations show a peculiar similarity between this light scattering and atomic-molecular scattering. A physical interpretation for these effects is given, based on an analogy of optics and quantum mechanics.

[Positive blood cultures in the "Centre des Brûles du c. h. u. de Lille". Evolution of epidemiology during the last thirteen years (author's transl)]. / Hémocultures positives au Centre des Brülés de Lille. Evolution épidémiologique des treize dernières années.

An epidemiological study was made on 3,249 patients admitted in the "Centre des Brûlés du C.H.U. de Lille" from January 1965 to December 1977. This study showed that 7.1 per cent of these patients has one or more positive blood cultures. The main bacteria are staphylococcus aureus, streptococcus, pseudomonias aeruginosa in spite of antibiotic therapy. Infection is the dangerous development in these patients of which generally a burned surface is more than 25 p.cent surface body.