Figure 4. The effect of halothane on metabolic rate in rats. (A) A typical recording of a control experiment with an unanesthetized rat (279 g). The responses to two norepinephrine injections are shown. (B) A typical recording from a halothane anesthetized, spontaneously breathing rat (285 gram). The halothane concentration was 1.5%. Fifty minutes of the recording have been omitted where indicated. (C) A typical recording from a halothane-anesthetized rat (310 g) in which the lungs were mechanically ventilated. Arterial blood samples (Table 1) were drawn at the indicated times 1–4 (sample 4 was drawn 20 min after sample 3). Thirty minutes of the recording have been omitted where indicated.