Figure 4-15 The nitrous oxide righting-reflex 50% effective dose (ED₅₀ ) values for male (closed symbols) and female (open symbols) offspring of mice selectively bred for resistance (HI group, circles) or susceptibility (LO group, triangles) to nitrous oxide anesthesia. The nitrous oxide requirements for HI and LO mice became progressively more separated over 15 generations of selective breeding. Standard errors about most points are less than 0.03 atm. Values for generations 1 through 10 are taken from references ^[8] and ^[174] .