Initial Respiratory Responses to the Intra‐tracheal Inhalation of Phosgene or Ammonia

The reflex responses to inhaled phosgene or ammonia vapour have been observed in tracheotomised dogs, cats and rabbits, and the most important findings are: ( a ) Ammonia and phosgene in high concentrations produce similar initial reactions, which are characteristic of each species and are mainly mediated by the vagi. ( b ) The dog appears to possess an extra‐vagal afferent system sensitive to such irritants, this system either being absent or much less sensitive in the cat and rabbit. ( c ) Bronchoconstriction is apparently induced by both gases in the absence of the central connexions of the vagus. 2. From studies on the isolated blood‐perfused lungs of dogs, it is found that ( a ) Bronchoconstriction is produced by inhalation of either phosgene or ammonia. ( b ) The bronchoconstrictor action of ammonia is specifically potentiated by eserine, an effect which can be reversed by atropine. ( c ) The stimulating action of greater‐than‐threshold doses of ammonia in non‐eserinized lungs is not affected by atropine, nicotine or anthisan. 3. From the evidence obtained in the second group of experiments, it is suggested that ammonia may have a direct stimulating action on the bronchial smooth muscle in addition to any action mediated by peripheral nervous structures and the release of acetylcholine.