THE successful results reported in the treatment of roden to cancer by the rays from radium, and the general germicidal action of the rays, make the discoveries and investigations by Prof. Rutherford of the radio-active emanations of radium and thorium of great possible importance to medical men. The present article deals with the manner in which these emanations can be inhaled into the lungs and be made the means of applying the rays from radium and thorium to the treatment of consumption, in the hope that medical men will be induced to undertake research in this field. The rays from radium and thorium are very similar in kind, but differ greatly in relative degree. Five minutes' application of radium would be about equivalent to ten years' application of the same weight of thorium. Both elements continually and spontaneously produce radio-active emanations, or gases in infinitesimal quantity, beyond the present means of chemical or spectroscopic detection, but endowed with very considerable powers of giving out rays on their own account of exactly similar kind to the rays from radium and thorium themselves. The best condition for the free escape of these emanations, so that they can mingle with the air the patient breathes, occurs with both radium and thorium compounds when they are dissolved in water. In the solid state the emanations are often stored up by the salt and do not escape. Three quarters of the normal activity of a dry solid radium compound is due to the stored up emanation. This escapes into the air instantly when it is dissolved in water.