A Convenient Source of Carbon Dioxid Snow

To the Editor:  —The treatment of certain dermatoses by carbon dioxid snow—a substitute originally suggested by Dr. Pusey for the less easily obtainable and less easily managed "liquid air"—has now an established place in the armamentarium of the dermatologist. Its common source is from the large cylinder of carbon dioxid furnished to soda-water fountains. This cylinder, although probably the cheapest source, is large, bulky, cumbersome and unsightly for office use, besides being somewhat clumsy for handling. I have recently found a convenient substitute for this; it is the small cylinder containing liquefied carbon dioxid sold for the inflation of a single automobile tire. It contains sufficient liquefied gas for a large tire—a sufficient quantity, as I have found, to produce enough "snow" for one average dermatologic application. This cylinder is about one inch in diameter and twelve inches in length; it costs $1, and when empty is returnable, being credited