Fig. 2.

(a), The response of the fundal strip to doses of 3-hydroxytryptamine (HT) in nanograms (ng.). The drum was left running continuously to illustrate the cycle. The second dose of 4 ng. HT shows the slowness of relaxation if the tissue is not stretched. (b), A more sensitive preparation showing responses down to 50 picagrams (pg.) HT, with an injection of 0.2 ml. saline at the end. For this and subsequent figures, a 5 ml. bath containing rat uterus Ringer at 37° was used. The lever, of magnification 16:1, is described in the text. The bath is washed out by overflow at the beginning of each downstroke. The vertical scale is in cm. Time in min.