Experiments on the bactericidal properties of mists were performed in a closed room of 850 cu. ft. capacity. The test organism was sprayed into the room through an Atmozon nebulizer operated from a mechanically driven Austin diaphragm compressor; the pressure was maintained at 7 lb./sq. in. Air to the compressor was taken through rubber tubing from an adjoining room to avoid accidental admixture of antiseptics into the air used to atomize the bacteria. The output of the nebulizer was 0·22 c.c./min. In the majority of the experiments the test organism was sprayed for 2 min. To ensure that an adequate mist was being emitted, the culture was nebulized in the dark against a dark background, and examined frequently with a light beam. Even distribution of the mist in the room was ensured by convection currents from a large hot-water pipe which ran along the length of two walls about 2 ft. from the floor, and by a small electrically driven fan placed immediately behind the nebulizer.