1. An aqueous solution of safranin precipitates the virus of tobacco mosaic from juice of diseased plants. This precipitate brings down practically all of the virus. The virus is apparently held in an inactive condition in the precipitate, but is released when the safranin is removed by means of amyl alcohol. 2. Material, which gives an infectious solution when redissolved in water, has been salted out of infectious juice with ammonium sulphate and also with magnesium sulphate. 3. Two volumes of acetone or alcohol, when added to one volume of juice from diseased plants, at about 0⚬ C., throws down a precipitate which contains practically all of the virus. 4. Juice from Turkish tobacco plants with mosaic disease contains two well defined heat precipitable fractions. One comes down around 85⚬ C. and the other above 90⚬ C. Only the first fraction contains an appreciable amount of nitrogen. The juice remains infectious after removal of the first fraction, although the virus concentration is greatly reduced. 5...