Drs. Wolfsdorf, Swift, and Avery1 have carried out an interesting study of the delivery and distribution of aerosolized water in the respiratory tract of adult humans. We do not doubt the validity of their data with the experimental design utilized. It is unfortunate that their design does not reproduce either the usual clinical setup for direct inhalation from a nebulizer or for inhalation from a mist tent. The usual mist tent is not air-tight. The fact that diffusion of air into and of oxygen out of such a tent occurs very rapidly is apparent to anyone who has attempted to raise the oxygen concentration above 50% by adding oxygen.