ConclusionsIntraperitoneal injection of amytal did not decrease the variability in the rate of oxygen consumption between different rats. Subcutaneous injection of the drug decreased this variability so that average results of a given standard deviation of the mean could be obtained with approximately half as many rats under anesthesia as would be required with non-treated rats. It is questionable whether or not this decrease in variability justifies the application of anesthesia in respiration trials since this application may introduce influences on metabolism tending to make the results less conclusive in many cases even though the variability may be decreased. The application of the anesthetic also makes the metabolic rate dependent on the time after injection so that a result on an anesthetized rat is not conclusive unless the time after the injection and its influence on the rate of metabolism are defined.