Figure 1. Log dose-response curves of morphine (MS) and clonidine (CL) combined at proportions of 1:3 (triangles), 1:1 (circles), and 1:0.33 (squares). The abscissa represents the sum of the doses of morphine and clonidine (measured in milligrams per kilogram), and the ordinate the percentage inhibition of gastrointestinal transit. Each point is the mean +/- SEM of ten or more mice.