A BEVIEW of present knowledge as to the liability of users of mercury to contract mercury poisoning by continued exposure to mercury vapour or to solutions of mercury compounds of small concentration has recently been issued (Rev. Sci. Inst., Aug.). Although there are great differences in the sensitivity to poisoning amongst individuals, it seems certain that prolonged exposure to an atmosphere containing one quarter of a milligram of mercury vapour per cubic metre of air is dangerous. As the saturation vapour pressure of mercury at 18° C. is such that there is more than 10 mgm. of mercury in a cubic metre, it is evident that exposure of considerable surfaces of mercury to air at ordinary temperatures should be avoided. Good ventilation is the best precaution where exposed surfaces are unavoidable, and this failing, gas masks containing carbon-iodine absorber should be used. Rubber gloves should be worn to prevent contact with mercury or mercury solutions.