ABSTRACT
The significance of skin ventilation to cutaneous gas exchange in vertebrates has seldom been recognized. Unlike the lungs and gills, the skin lacks a dedicated ventilatory pump, and most analyses have implicitly or explicitly ignored skin ventilation because the skin is in contact with an ‘infinite pool’ (Piiper & Scheid, 1977) of respiratory medium. For example, models of gas exchangers consider amphibian skin to have an infinite ventilatory conductance (e.g. Piiper & Scheid, 1977) and in experimental studies the respiratory medium is often stirred thoroughly (e.g. Gottlieb & Jackson, 1976; Burggren & Moalli, 1984), which may eliminate any impact of ventilatory inadequacy upon cutaneous gas exchange. Indeed, as discussed by Piiper (1982) and Feder & Burggren (1985), most previous analyses have not accounted for ‘stratification’ or ‘diffusion boundary layers’ about the skin, which theoretically may limit cutaneous gas exchange, especially in still water. Skin ventilation may be important in dissipating such boundary layers, and several skinbreathing vertebrates have particular behaviour patterns that might serve this function (reviewed by Feder & Burggren, 1985). However, there is no direct experimental evidence that the movement of respiratory medium across the skin can affect cutaneous gas exchange.
