CARBONIC ACID SNOW. Carbon dioxide under heavy pressure in cylinders is allowed to escape into a suitable cylindrical receptacle the diameter of which varies according to the size of the lesion to be treated. A semi-solid snow is formed and this can be compressed into a pencil. The pencil, covered with a towel or cotton wool to protect the operator's hands, is cut to a suitable size and then applied to the lesion, such as a naevus, port-wine stain or lupus patch. If the lesion be small, the pencil should cover the whole of it when pressed down ; if large, an area about one inch in diameter should be treated at a time. Each applica tion of the pencil should last from about half a minute to one minute.