Evaluates the effects of halothane, enflurane, isoflurane and sevoflurane on slowly adapting pulmonary stretch receptor (SAR) activity in dogs. Two different types and pulmonary location of SAR; Responses of SARs to inhalation of anesthetics; Measurement of minimal alveolar anesthetic concentration; Several factors that influence the spontaneous activities, discharge patterns and excitation thresholds of SARs.