Fig. 1

Sequential plot and histograms of inspiratory period for an en bloc in vitro preparation of rat brain stem before and after treatment with an opiate agonist, showing quantal slowing down of inspiration (reproduced with permission from [2]). The horizontal axis on the sequential plot is “cycle number” (meaning number of inspirations since a start time), the vertical axis is time between successive inspirations in seconds. The horizontal axis for the histograms is inspiration period and the histograms are plotted for ten different experiments. When the potassium concentration was increased in two experiments (the last two histograms, in red), the slowing of the inspiratory period was no longer quantised