INSPECTION OF THOKACIC CONTENTS 19 



left side and make out the meeting of the sup. and inf. venae cavae with the 

 right auricle. Take the heart gently between fingers and thumb and feel the 

 hardening of the ventricles, especially of the left, at systole. Pass threads 

 cautiously round (1) superior cava, (2) inferior cava, (3) pulmonary artery, and 

 (4) aoi-ta. Observe thoroughly the effects of partially or completely occluding 

 for a few seconds each of these vessels by drawing on its thread. Notice the 

 extensibility of the aortic wall as shown by the swelling up of the vessel on 

 the proximal side of the occluding ligature ; also its elasticity as shown by 

 its return on releasing the thread. Carefully replace the sternal flap over the 

 thorax. 



VIII. Make a lengthwise incision (PI. II, figs. 1, 2, 3, 4) for 4 cm. along Obs. 13. 

 the right side of the neck, starting about 1 cm. from the mid-line at the level laspection of 

 of the cricoid cartilage, which can easily be felt. Draw to the right with a Qf\^ heart'b 

 weighted clip the medial edge of the muscle, sterno-mastoid, exposed through the vagus, 

 the wound. The vagus nerve will be seen lying beside the carotid artery ; 

 another nerve, much smaller, the cervical sympathetic, accompanies the 

 vagus. Free the vagus nerve carefully by separating from it the other 

 structures with fine forceps and scalpel ; the nerve itself must not be injured, 

 least of aU picked up with the forceps. Under its upper freed course pass a 

 thread by means of a blunt curved mounted needle. Ligate the nerve and 

 cut it across with fine scissors headward of the ligature. Lifting the nerve by 

 the ligature, dissect its distal part downward towards the thorax and free it 

 from all suroundings for at least 2 cm. Bring the stimulating apparatus to a 

 convenient position for exciting the nerve by the hand-electrodes, the 

 secondary coil of the inductorium being at 12 cm. on the scale. 



Raise the sternal flap and hook it back so as to bring the heart into full 

 view. Apply the electrodes to the nerve-trunk well lifted from the wound ; air 

 insulation guards against escape of the exciting current to other structures than 

 the nerve. The nerve and electrodes should be so held (PI. II, fig. 3) that one 

 terminal of the electrodes touches the nerve on one side and the other touches 

 it on the other. The equal passage of the current through the whole thickness 

 of the nerve-trunk is thus favoured. After the electrodes are in position, get 

 your co-worker to open the short-circuiting key in the second circuit, the 

 current and interrupting hammer in the primary having been already started. 

 Note the slowing of the heart-beat ; the slowing may be pushed to temporary 

 complete arrest by repeating with the secondary coil nearer the primary. 

 Each stimulation should not be prolonged beyond 5". 



Using a stimulus strong enough to completely arrest the beat, keep it 

 applied for a longer period and note that after a varying time the ventricle 



D 2 



