PULMONARY NERVES. 



^Lechanism of the Influence of the Pneumogastrics upon 

 the Action of the Heart. It is useless to speculate upon the 

 exact mechanism of the action of the pneumogastrics upon 

 the heart. Although various explanations have been pre- 

 sented of the effects following division of the nerves in the 

 neck, and of the opposite phenomena which attend the gal- 

 vanization of their peripheral ends, they are all more or less 

 unsatisfactory. All that can be said, in the present state of 

 our knowledge, is, that the pneumogastrics have a direct in- 

 hibitory influence on the heart. When they are divided, 

 and the heart is removed from their influence, the pulsations 

 become more rapid. When the peripheral ends of the di- 

 vided nerves are galvanized, the heart beats more slowly, or^ 

 its action may be arrested by .a current of sufficient power. 

 This action may also be reflex, due to an impression con- 

 veyed to the centres by what have been described by the 

 brothers Cyon and Ludwig, as the depressor-nerves. 



Properties and Functions of the Pulmonary Branches, 

 and Influence of the Pneumogastrics iipon Respiration. 

 The trachea, bronchi, and the pulmonary structure are 

 supplied with motor and sensory filaments by branches of 

 the pneumogastrics. The recurrent laryngeals supply the 

 upper, and the pulmonary branches, the lower part of the 

 trachea, the lungs themselves being supplied by the pulmo- 

 nary branches alone. The sensibility of the mucous mem- 

 brane of the trachea and bronchi is due to the pneumogas- 

 trics, for these parts are insensible to irritation when the 

 nerves have been divided in the neck. Longet has shown 

 that, while an animal coughed and showed signs of pain 

 when the mucous membrane of the respiratory passages was 

 irritated, after division of the pneumogastrics there was no 

 evidence of sensibility, even when the tracheal mucous mem- 

 brane was treated with strong acid, or even cauterized. He 

 also saw the muscular fibres of the small bronchial tubes 



