CARDIAC AND PULMONARY NERVES 539 



The obstruction to the entrance of air into the lungs is a sufficient 

 explanation of the increase in the number of the respiratory acts 

 after division of both recurrents. The acceleration of respiration is 

 much greater in young than in adult animals. This does not apply to 

 very young animals, in which section of the recurrents produces almost 

 instant death. 



Feeble stimulation of the central ends of the inferior laryngeals, 

 after their division, produces rhythmical movements of deglutition, coin- 

 cident usually with arrest of the action of the diaphragm. These phe- 

 nomena are commonly observed in rabbits, but they are not constant. 

 The reflex action of these nerves in deglutition probably is dependent 

 on the communicating filaments which they send to the superior laryn- 

 geal nerves. 



Properties and Uses of the Cardiac Nerves. The chief uses of the 

 cardiac branches relate to the influence of the pneumogastrics on the 

 action of the heart. This has already been considered in connection 

 with the physiology of the circulation. The effect of dividing the pneu- 

 mogastrics in the neck is to remove the heart from the influence of its 

 inhibitory nerves ; but at the same time the operation profoundly affects 

 the respiratory movementSj and this latter effect must be eliminated 

 so far as possible in studying the influence of the pneumogastrics on 

 the circulation. The same remark applies to the experiment of faradiz- 

 ation of the pneumogastrics in the neck. The cardiac branches are 

 operated on with difficulty, and most experiments have been made on 

 the cervical portion of the pneumogastric itself. 



Faradization of the pneumogastrics in the neck arrests the action of 

 the heart in diastole. This is a direct action and is due to the excita- 

 tion of the inhibitory fibres, which are derived from the spinal accessory 

 nerves. The phenomena following stimulation of these nerves have 

 already been described in connection with the physiology of the circu- 

 lation and the properties and uses of the spinal accessories. 



Depressor Nerve. While this nerve is not isolated in the human 

 subject, it is probable that fibres, the action of which is analogous to 

 that observed in animals in which the nerve is anatomically distinct, 

 exist in the trunk of the pneumogastric. The action of the depressor 

 nerves, which is reflex, has already been described in connection with 

 the physiology of the circulation. 



Properties and Uses of the Pulmonary Nerves. The trachea, 

 bronchia and the pulmonary structure are supplied with motor and 

 sensory filaments by branches of the pneumogastrics. The recurrent 

 laryngeals supply the upper part, and the pulmonary branches, the lower 

 part of the trachea, the lungs themselves being supplied by the pulmo- 



