1. Block of the phrenic nerves in three normal subjects, produced by injection of lignocaine in the neck, caused alleviation of the thoracic sensation during breath holding and prolonged breath-holding time. 2. Injection of lignocaine in the neck without nerve block had no effect on breath holding sensation or breath-holding time. 3. A patient with a spinal-cord transection at the third cervical segment with paralysed diaphragm and chest wall, had no sensation in the chest or abdomen during breath holding. 4. This patient maintained normal ventilation by using hypertrophied sternomastoid muscles. During breath holding he experienced no sensation in the neck despite the presence of sternomastoid contraction. 5. There is previous evidence that complete muscular paralysis abolishes breath-holding sensation but that paralysis of all muscles innervated from spinal segments below the eighth cervical has no effect.
1. The effect of lung deflation was studied during treatment of patients for spontaneous pneumothorax: (a) in four patients acute lung deflation was produced by opening the chest drain to the atmosphere and the immediate effect on breathing was observed and (b) breath-holding time and the ventilatory response to CO 2 were determined on admission to hospital and after recovery in a further four patients. 2. Allowing one lung to deflate suddenly produced an immediate increase in respiratory rate and electrical activity in inspiratory muscles. 3. Maximum breath-holding times were always decreased by pneumothorax. 4. In the presence of pneumothorax, the ventilatory response to rebreathing CO 2 was increased at the break point, the respiratory rate was increased and the P co 2 at the breakpoint decreased in three out of four patients. 5. These results are consistent with the hypothesis that lung deflation has a reflex excitatory effect on breathing (Hering—Breuer deflation reflex). If this hypothesis is correct, it would appear that the threshold for the reflex is higher than for other mammalian species.