The response of foetal sheep and lambs to pulmonary inflation.

1. Pulmonary inflation through a tracheostomy consistently produces an inspiratory response or gasp in the foetal lamb. This response is reversibly removed by vagal cooling or xylocaine local anaesthesia to the air passages. It is abolished by bilateral vagotomy. It is therefore suggested that this gasp response involves a reflex whose afferent pathway is in the vagus nerve.2. This gasp reflex is also found in lambs aged 1 hr to 30 days.3. Lambs and foetuses possess a cough reflex.4. A Hering-Breuer inflation reflex can be demonstrated in lambs.5. The gasp reflex is distinct from either of these last two.6. The significance of the gasp reflex in pre- and post-natal life is discussed.