BY DR. BURDON-SANDERSON. 283 



the ganglia of the cord sends towards the mescnteric artery a 

 branch which meets with its fellow from the corresponding 

 ganglion of the opposite side, to form a plexus of nerves 

 which surrounds the artery ; and that from or through this 

 plexus a nerve or nerves (nervi mesenterici) can be traced 

 which follow the vessel towards its distribution. It is in these 

 nerves that the fibres which are in reflex relation with the 

 vagus are contained. To excite them, the best method is to 

 raise the aortrc with the forceps from the bodies of the verte- 

 bne, drawing upwards with them at the same time the two 

 ganglionic cords; then to divide the abdominal aorta and the 

 two cords at the level of the seventh or eighth vertebra, sever- 

 ing at the same time some of the rami communicantes on 

 either side; and lastly, to place the two aortse and the cords 

 which accompany them, on the excitor in such a position that 

 the two ganglia next the junction are in contact with the 

 electrodes. On opening the key, the heart is arrested in dias- 

 tole, beginning to contract again rhythmically as before, when 

 the excitation is discontinued. To demonstrate that the 

 channels by which stimulation of the mesenteric nerves affects 

 the heart are the vagus nerves and their centres in the me- 

 dulla oblongata, the experiment must be thrice repeated; first, 

 after section of both vagi ; secondly, after destruction of the 

 medulla oblongata; and thirdly, after destruction of the brain, 

 the medulla remaining intact. In the first and second cases 

 the effect is annulled, in the third it is unaltered. 1 



77. Reflex Excitation of the Vagus of the Frog, by 

 Mechanical Means: Goltz's Klopfversuch. It is now 

 man}' years since it was discovered by Goltz that excitation of 

 the ends of the mesenteric nerves by mechanical means produces 

 the same effect as the electrical excitation of their trunks. To 

 show this, a frog is secured on its back, the pleuro-peritoneal 

 cavity opened, and the heart exposed as before. The surface 

 of the intestine is then smartly tapped. After a few moments 

 the heart is arrested in diastole. If the ganglionic cord is then 

 divided on each side opposite the junction of the two aortae, and 

 the experiment repeated, no effect is produced. Another frog 

 is prepared in the same way, with the exception that both vagi 

 are divided. On repeating the tapping, the result is negative. 

 The same thing happens if, instead of dividing the vagi, the 

 cord is divided immediately below the medulla. 



78. Reflex Excitation of the Vagus in Mammalia. 

 The constant action of the inhibitory heart nerves in the higher 

 animals is dependent on the constant action of the centripetal 

 nerves in reflex relation with them. This may be shown as fol- 



1 " Untersuclmngen iiber don Mechanismus cles regulatorischen Herz- 

 nervensystems." Archiv f. Anat, u. Physiol., 1804, p. 614. 



