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The question formulated in the introduction to this report can now be answered. Ozone in tolerable concentration is able to inactivate certain bacteria when these are present as unprotected singleton aerosol particles in atmospheres of 60–90% R.h. When such bacteria are covered with a protective coating of organic matter, however, as in aerosols naturally emitted during a sneeze or cough, then ozone in permissible concentration is without significant effect. Inactivation of such protected organisms can only be achieved by the use of ozone in decidedly higher concentrations, which must be deemed dangerous for prolonged spells of breathing. Bacteria that have settled on surfaces are generally more resistant to ozone than when in newly formed aerosols. Hence experimental evidence leads to the conclusion that ozone, in concentrations that can be breathed over long periods without irritation, cannot be expected to provide any effective protection against air-borne bacterial infection, through direct inactivation of the infectious carrier particles.

SUMMARY:Influenza and related viruses were studied by a new method in which virus is adsorbed on the membranes of laked fowl red cells for examination in the electron microscope. The numbers of virus particles adsorbed per unit area of red-cell membrane were estimated from direct counts in micrographs of palladium-shadowed and unshadowed specimens. There was a definite saturation level of adsorption for each strain of virus, the value varying also according to the particular batch of cells and their age after storage at 0". For subsaturation conditions the number of particles adsorbed was proportional to the concentration of virus and the concentration of cells, and a function both of time of contact and temperature. The relationships were complicated by the fact that elution began before adsorption was complete.The comparative data for the size and variation of these viruses were obtained from micrographs of preparations directly adsorbed from infective allantoic fluid and thus not subjected to harsh methods of purification. The mean sizes (mp) found for the dried virus were : influenza A virus, 90 11.5 ; influenza 13 virus, 103 k 8 ; fowl-plague virus, 101 f 16 ; Pu'ewcastle-disease virus, 193 f 28 ; and mumps virus, 179 f 28.The occurrence of long forms associated with influenza B virus was confirmed and filamentous structures were demonstrated for the first time in preparations of a strain of fowl-plague virus.

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1. A method is described for the experimental investigation of aerosol systems formed by the atomization of suspensions of viruses into the atmosphere. Observations on the physical properties of such systems have been made, and an experimental approach found to certain practical problems connected with air-borne virus infections, particularly counter measures involving the use of ultra-violet light and aerosols of chemical antiseptics.2. Mice, placed in an atmosphere into which the respective virus had been atomized, have contracted the diseases of influenza and infectious ectromelia in a manner closely analogous to naturally occurring air-borne infection.3. The infection resulting from the inhalation of virus is described. The suggestion is made that this method of infection may be used with advantage (a)in studying in detail the histology of lung lesions, and (b) in obtaining more uniform infection of large batches of mice.4. The two methods of experimental infection, (i) intranasal instillation under anaesthesia, and (ii) normal inhalation, have been compared and contrasted. It is deduced from the evidence available that as little as 1 % only of the virus may reach the lungs of mice breathing normally in an atmosphere containing dispersed nuclei of influenza virus.We gratefully acknowledge the assistance we have received from Miss Dora Lush.