Experiments have been reported on the prevention of air-borne infectionin white mice, conducted in a large hospital ward (14,000 cubic feet) subdivided into sixteen separate cubicles. Groups of animals were placed in some of the locations, while cultures of the hemolytic streptococcus of Lancefield's Group C or of the virus of influenza A were atomized in one of the cubicles. Both organisms spread rapidly throughout the air of the ward. Ultraviolet irradiation and propylene glycol vapor were compared in their effectiveness as disinfectants of the air.

With heavy concentrations of air-borne streptococci (more than 3,000 cells per cubic foot of air) most of the control mice died from streptococcal pneumonia and septicemia, while propylene glycol vapor protected them completely and ultraviolet irradiation failed to prevent death only in the cubicle containing the atomizer.

With low concentrations of the streptococcus (200 to 500 organisms per cubic foot of air), all mice survived and cultures taken from the lungs on the eighth or tenth day failed to reveal the streptococcus. However, it could be shown in other experiments that a carrier state had been induced in the animals exposed under control conditions, and not in those protected by ultraviolet light barriers. This was demonstrated by inoculation of the virus of influenza A eight to ten days after exposure to the air-borne streptococcus. All mice died from influenza, but only those belonging to the control group now showed hemolytic streptococci in cultures taken from the lungs. Instillation of sterile broth only occasionally activated the streptococcus in the carrier.

Ultraviolet irradiation and propylene glycol vapor were similarlyeffective in preventing the air-borne infection with the virus of influenza A. While all control mice succumbed to the disease, propylene glycol vapor protected the animals completely against death and only a few lesions were noted in animals from the cubicle containing the atomizer. More lesions and several deaths were observed in the same cubicle when the air was irradiated by ultraviolet lights, and pulmonary involvement was noted also in other locations close to the atomizer, under the same conditions.

These results indicate that both ultraviolet light and propylene glycolvapor are effective disinfectants of the air. Their application will depend upon the individual problems and the location to be disinfected. It must be re-emphasized that only infection by droplet nuclei has been studied. Flügge droplet and possibly dust-borne infections may require different means of control.