Fig. 2. The traditional diagram depicting the mechanism for the second gas effect in a simplified model of the lung with an inspired nitrous oxide (N2O) concentration of 80%, 19% oxygen (O2), and 1% “second gas” ( left ). The increase in the concentration of the oxygen and second gas is shown to the right , where half of the inspired volume of nitrous oxide is taken up by blood ( heavy lines at bottom ). The concentrations of the gases in blood leaving the lung are shown at the bottom .