ACTION OF ETHER ON THE HEART 65 



EXPERIMENT II. 



Ether. (Action on the Heart. Dissection for the Vagus 



Nerve in the Frog.) 



1. Pith a frog and clamp it down to the board with the 

 central side up, as shown in Fig. 60. With sharp scissors 

 split the abdominal and thoracic walls in the median line 

 forward into the skin over the floor of the mouth. If pos- 

 sible avoid dividing the abdominal vessels. Cut open the 

 girdle of bones directly over the heart (which should be 

 carefully avoided) with the scissors. Then pull the tho- 

 racic cavity widely open by stretching out the fore legs from 

 side to side. Reset the clamps holding these legs. Refer 

 to Fig. 60 and identify the glossopharyngeal, hypoglossal, 

 and brachial nerves. Near the angle of the jaw dissect 

 down carefully with a probe and fine-pointed forceps until 

 the laryngeal branch of the vagus and the vago-sympathetic 

 nerves come into sight. For the method of union between 

 the sympathetic chain and the main trunk of the vagus 

 nerve see Fig. 61. The sympathetic fibers pass forward 

 in the thorax to the base of the skull where they turn back- 

 wards and unite with the vagus nerve to be distributed 

 ivith the vagus to the heart, lungs, etc. When, the vago- 

 sympathetic nerve has been found it should be pulled out- 

 ward a little and the points of the electrodes slipped be- 

 neath the nerve. With a tetanizing current of medium 

 strength stimulate the nerve and see if the heart stops. 

 This is to identify the nerve. Do not stimulate lite nerve 

 any longer tlian is absolutely necessary, for the nerve end- 

 ings are easily fatigued and may not be able to stop the 

 heart later after your apparatus is all arranged. 



The heart is now freed from the pericardium and con- 

 nected with a heart lever by means of a pin hook and a 

 thread as shown in Fig. 63. The tip of the ventricle is at- 

 tached to the pericardium by a small ligament called the 



