Substantial reduction in the bacterial content of the air of an empty room after infection with B. prodigiosus (or with Staphylococcus albus or a diphtheroid bacillus) has been effected by means of hypochlorites introduced into the air by atomization from a Dynalysor or by spraying from a flit gun.The ‘normal’ variation of the bacterial content of the air of an occupied (crowded) room has been described.Repeated spraying of a solution containing 1% of sodium hypochlorite or of a 1·3% suspension of water-sterilizing powder (bleaching powder) from a flit gun has been shown to reduce materially the bacterial content of the air of the occupied room.Similar sprayings of water have been shown to have no appreciable effect on the bacterial content of the air of the occupied room and the action of the hypochlorite was, therefore, not merely a mechanical removal of bacteria from the air.Methods have been devised for assessing the degree of disinfection per individual spraying of hypochlorite, and, although the methods are mainly of comparative value, it may be stated that the reduction in the total bacterial content of the air of the occupied room for a single spraying of hypochlorite Y (≡1% sodium hypochlorite) was of the order of 33%, or more. The percentage reduction of potentially pathogenic bacteria which may have been present was almost certainly greater than the reduction of the total bacterial content, which included resistant saprophytic bacteria. The average concentration of hypochlorite Y used in these experiments was 0·38 c.c. per million c.c. of air (i.e. less than 11·0 c.c. per 1000 cu. ft. of air) per spraying, i.e. was exceedingly small, and even smaller concentrations were equally effective when the hypochlorite was atomized into the air by means of the Dynalysor.Rather less consistent results were obtained with the chemically less active bleaching powder suspension than with hypochlorite Y in the flit-gun experiments.The relative humidity of the air has been shown to be a factor of great importance, and in the experiments described in this paper effective air disinfection was not obtained at low relative humidities at temperatures ranging from 54 to 74° F. The need for accurate determination of the critical lower limit of relative humidity is stressed.Tobacco smoke has been shown to reduce the efficiency of hypochlorite sprays but the experimental evidence was insufficient for any definite conclusion to be drawn.The advantages and disadvantages of hypochlorites as air disinfectants have been discussed and the conclusion reached that repeated (every 20 or 30 min.) spraying of the air of an occupied room with a 1% solution of hypochlorite (e.g. hypochlorite Y) constitutes a simple, practical, inexpensive and efficient method of air disinfection, and, provided simple precautions are observed, there are no serious objections to such a procedure.
