CARDIAC NERVES. 223 



deglutition is probably due to the communicating filaments 

 which they send to the superior laryngeal nerves. 



Properties and Functions of the Cardiac Nerves, and 

 Influence of the Pneumogastrics upon the Circulation. One 

 of the most interesting questions connected with the physi- 

 ology of the pneumogastric nerves is their action upon the 

 heart ; and the results of experiments, which will be fully 

 detailed hereafter, are precisely the opposite of what would 

 be expected in the case of a nerve containing motor fila- 

 ments and distributed to a muscular organ. . Section of the 

 pneumogastrics in the neck, far from arresting the action of 

 the heart, increases the rapidity of its. pulsations; and gal- 

 vanization of the nerves arrests the heart's action in diastole. 



TV"ithin the past few years, some very remarkable experi- 

 ments have been made upon the influence of certain nerves 

 given off near the superior laryngeals, which have been 

 called the depressors of the circulation ; but most observa- 

 tions have been made upon the trunks of the pneumogastrics 

 in the cervical region, as it is exceedingly difficult to isolate 

 the thoracic cardiac branches and to operate upon them with- 

 out involving other nervous filaments. In galvanizing the 

 nerves in the neck, we have to consider both the direct 

 influence of the current and the phenomena due to reflex 

 action. 



Effects of Section of the Pneumogastrics upon the Circu- 

 lation. It is not necessary to cite in detail the various ex- 

 periments upon the effects of section of the pneumogastrics 

 in the neck upon the action of the heart. The division of 

 these nerves in living animals is sufficiently easy, and all 

 who have performed the operation have noted the same re- 

 sults. By section of these nerves, the heart is at once sepa- 

 rated from one of the most important of its nervous connec- 

 tions ; and the effects show that, as far as this organ is con- 

 cerned, the motor filaments present great differences from 



115 



