LESSON XXI 

 THE CIRCULATION (Continued) 



THE EFFECT OF DIVISION AND STIMULATION OF THE VAGUS NERVE 

 UPON THE BLOOD-PRESSURE AND ACTION OF THE HEART 



1. Stimulation of the Intact Vagi Nerves. Etherize a mammal and 

 continue the anesthesia until the animal has been killed at the end of 

 the following experiments: Perform tracheotomy. Listen to the heart 

 sounds and locate the cardiac impulse. With the tips of your index- 

 fingers press gently upon the skin of the neck overlying the vagi nerves. 

 Do you notice a reduction in the rate of the heart? Expose the com- 

 mon carotid artery on the left side and insert in it a straight cannula 

 to be connected later on with the mercury manometer. Also expose the 



FIG. 73. RECORD OF CAROTID BLOOD-PRESSURE. 



S, Stimulation of left vagus nerve. The fall in pressure is followed by compensatory 

 changes before the normal pressure is again established. 



common carotid artery on the right side, and separate both vagi nerves 

 from the sheaths of these blood-vessels. Place each in a loose silk 

 ligature. Arrange the stimulating apparatus to yield a quickly inter- 

 rupted current of medium strength. 



Apply the electrodes to the left intact vagus and stimulate briefly, 

 while the normal blood-pressure is being recorded. In case the effect 

 is too indefinite, increase the strength of the current slightly. Test 

 the opposite nerve in the same manner and with the same strength of 

 current. Do you notice a difference in the inhibitor power of these 

 nerves? In each case allow the pressure to return to normal before you 



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