CHAP. XX.] THE VAGUS NERVE. 123 



the whole tube to the cardia, where they became slow and vermi- 

 cular ; the oesophagus being shortened and diminished in calibre at 

 each application of the irritant. 



Distinct palsy of the oesophagus may be produced by section of 

 the vagus in the neck. The following effects followed this experi- 

 ment by Dr. Reid on a rabbit, which had been kept fasting for sixteen 

 hours previous to the experiment. The animal ate a quantity of 

 parsley, amid considerable dyspnoea and cough, with many efforts 

 to vomit. It died in five hours. The oesophagus was found full of 

 parsley throughout its entire extent down to the stomach, which was 

 also filled) although not distended; and a good deal of the parsley 

 had passed into the trachea and bronchial tubes, and even into the 

 minute air-cells of the lungs. 



The appearances in this experiment indicated complete paralysis 

 of the oesophagus. This tube was filled by the propulsive power of 

 the pharynx, which sent on morsel after morsel until the whole 

 stomach and gullet were filled, the latter being perfectly passive : 

 and after these parts were occupied, and thus resisted the further 

 passage of the parsley, it found its way more readily into the larynx 

 and trachea. 



It may be inferred from this and similar experiments that some- 

 thing more than an irritable condition of the muscular coat of the 

 oesophagus is requisite in order to insure its contraction when dis- 

 tended by food. 



The muscular fibres were quite uninjured, and, therefore, ought 

 to have acted, if the stimulus of distension were alone sufficient to 

 excite their contraction. The true cause of their inaction was the 

 destruction of the nervous circle through which the sensitive nerves 

 of the oesophagus could excite its motor nerves. This portion of 

 the act of deglutition, therefore, is like that in the pharynx, a physical 

 action, brought about by the impression of the food upon the sentient 

 nerves of the oesophagus, which propagate their change to the cen- 

 tre where the motor fibres become excited. It cannot be said, how- 

 ever, that the mind is unconscious of this part of the act of degluti- 

 tion, although it may be reasonably admitted that it has no necessary 

 share in it. 



The results of section of the cardiac nerves show that, these 

 nerves exert only a partial influence upon the heart: the de- 

 struction of them affects the actions of that organ only to a limited 

 degree, inasmuch as the heart receives nerves from the sympathetic 

 as well as from the vagus. 



Numerous experiments demonstrate most unequivocally that this 



