A mathematical expression for oxygen-induced death of dehydrated bacteria is reported. Data in the literature for Serratia marcescens SUK were analysed and the expression describes viability changes over a range of lo4, oxygen concentration effects over a range of 400 and the effect of time up to 3 h. The expression should apply to the oxygen-induced death of other dehydrated bacteria.

1974. Aerosol survival of Serratia tnarcescens as a function of oxygen concentration, relative humidity, and time. Can. J. Microbiol. 20: 1529-1534 Previously the kinetics of loss of viability of freeze-dried Serratia r?~arcesce7u 8UK were determined by Cox and Heckly as a function of oxygen concentration and time. Results are presented here when dehydration is brought about by aerosolization into atmospheres of low relative humidity (RH) rather than by freeze-drying. As for freeze-dried S . marcescens, oxygen was toxic and viable decay followed the same kinetics with respect to oxygen concentration and time. The influence of R H upon viable decay (which was not studied in the previous report) was that above 65% R H oxygen was not toxic but was progressively more toxic as the humidity was further reduced. Kinetic analyses of the results indicate that the site for the toxic action of oxygen lies in the interspace between the cytoplasmic membrane and the cell wall. Such a finding is consistent with other data which suggest that cell division and (or) cell wall synthesis in bacteria are inhibited by oxygen.Cox, C. S., S. J. GAGEN et J. BAXTER. 1974. Aerosol survival of Serratia marcescens as a function of oxygen concentration, relative humidity, and time. Can. J. Microbiol. 20: 1529-1534. Cox et Heckly anterieurement ont determine la cinetique de la perte de viabilitt de cellules IyophilisCes de Serratia marcescens 8UK en fonction de la concentration d'oxygene et du temps. Nous presentons ici des resultats o i~ la dkshydratation est amenCe par l'atrosolisation dans des atmospheres de faible humidit6 relative au lieu que par lyophilisation. Comme pour les cellules lyophilistes de S. marcescens, l'oxygene est toxique et le decroissement de la viabilite suit la m&me cinetique en regard de la concentration d'oxygene et du temps. L'influence de l'humidite relative sur la viabilite (laquelle n'a pas CtC determinee prCcCdemment) est que en haut de 65% de R H l'oxygene n'est pas toxique mais le devient progressivement lorsque I'humiditC est rCduite. Les analyses cinetiques des resultats indiquent que le site de l'action toxique de l'oxygene reside dans l'espace entre la membrane cytoplasmique et la paroi cellulaire. Cette conclusion est en accord avec d'autres donntes qui suggerent que la division cellulaire et (ou) la synthese de la paroi cellulaire chez les bactkries est inhibee par I'oxygene.[Traduit par le jouri~al]

Radon-222 and 222Rn progeny concentrations, barometric pressure and pressure differentials between inside and outside were measured continuously in the basement of a recently constructed energy-efficient house in metropolitan Denver, CO. Although the monitoring equipment was developed primarily for underground mines, it proved to be applicable for house monitoring. Results indicate that for tightly sealed houses, forced-flow transport does not significantly contribute to the 222Rn present even when the pressure within the house is less than the outside pressure by 0.8 Pa (.006 mm Hg). Calculations of 222Rn levels using diffusion as the primary transport mechanism are in agreement with observed data. The diffusion coefficient of 222Rn in the walls and floor surrounding the basement is higher than values previously reported. Ventilation by means of a heat exchanger reduces the 222Rn levels in accordance with measured air exchange rates, regardless of the pressure differential between inside and outside.

It is shown how concentrations of the open-air factor may be compared from day to day; this has not been possible previously.

It is shown how concentrations of the open-air factor may be compared from day to day; this has not been possible previously.