This thesis investigates the pattern of breathing, lung reflex responses and activity of vagal lung receptors in an animal model of emphysema. The specific aim was to investigate if changes in pulmonary receptor activity are produced in an animal model of emphysema, and if these can be related to any changes in breathing pattern and lung reflex responses occurring in the diseased model. Emphysema was induced in rats by an endotracheal instillation of the proteolytic enzyme papain (120 mg/kg body weight). In control and emphysematous anaesthetised rats the pattern of breathing during eupnoea and during administration of 4% and 6% CO₂ was measured. The reflex responses to lung inflation and deflation pressures of 5 and 10cm were also recorded. Activity was recorded from either slowly adapting (SARs) or rapidly adapting receptors, (RARs) in single fibres of the left vagus nerve during the above conditions. After bilateral vagotomy the pattern of breathing was measured in both groups of rats. The alveolar walls of the papain treated rats had a significantly increased mean linear intercept value of 109.3+/-2.7 μm compared to 81.5+/- 3.1 μm in the control rats, (P<0.01), indicating that emphysema had been induced. Breathing frequency in the diseased rats with the vagi intact was slightly slower than the controls. Tidal volume was similar in both groups of rats 2.85+/-0.2 ml in the emphysematous and 2.83+/-0.2 ml in the controls. Breathing 4% and 6% CO₂ increased tidal volume in both groups of rats although this response was more vigorous in the controls, breathing frequency was not significantly altered in either group. Without the influence of the vagi the diseased rats breathed slightly faster than the controls. The Hering-Breuer inflation reflex response to both 5 and 10cm. H₂O pressure was significantly longer in the emphysematous rats.