The Physiological Action of Epinephrin on the Bronchi

The earlier experimenters ( I ) in their work on the physiology of the bronchial muscles directed their attention to the effects of stimulation of the vagus. In most instances they used excised, but still living, preparations. They recorded the resulting changes in intrapulmonary pressure generally by means of a water manometer connected with the trachea. Their experiments, dating back to 184o, indicated with considerable uniformity that the result of vagus stimulation is constriction of the bronchi. While their experiments are valuable as a whole, the methods used are open to criticism. Einthoven (2) was the first to make accurate use of a new procedure, "a i r perfusion," which has .been the basis of the best subsequent experimentation in this direction. By rhythmically injecting air into the trachea of a living animal, he maintained a constant artificial respiration, and was able to determine variations in the size of the 'bronchi before and after stimulation of the vagus, through records of the changes in the maximal ( inspiratory)intratracheal pressure. He found that stimulation of this nerve produced constriction of the bronchi, but he obtained no evidence of any relaxing effect. As section of the vagi produced no change in his results, he concluded that normally the bronchial muscles are not in a condition of vagus tone. The first experiments concerning the effect of epinephrin on the bronchial muscles were conducted by Dixon and Brodie (3), though it should be remarked that their experiments with epinephrin represented only a small part of a larger work. They used living animals,