THE CIRCULATION OF THE BLOOD 97 



carefully upon the vagus and see that no unnecessary tension is 

 allowed to be exerted upon the nerve. It is usually necessary to 

 hold the electrode in place during the observations. 

 4. Observations, a. Anaesthesia. (Observations of Group "a.") 



(1) Are you able to make out the different stages of anaesthesia? 



(2) How many stages did your animal manifest? 



(3) Give the characteristics of each stage? 



(4) What effect did the ether have upon the rate of heart beat? 



(5) What effect did ether have upon respiration? 



6. The Stimulation of the Vagus. (Observations of Groups "c" 

 and "d.") 



(6) Stimulate moderately one vagus. Note with a stethoscope any 

 change in the rate of the heart. 



(7) Cut both vagi high up in the neck. Note the rate of heart 

 beat at intervals of five minutes for thirty minutes, allowing the 

 rabbit to partially recover from the anaesthesia. 



(8) Stimulate one vagus. Compare the result with that obtained 

 under experiment (6). 



(9) Will very strong stimulation bring the heart to a standstill? 



(10) "If the heart were brought to a complete standstill by the 

 stimulation, will it start up spontaneously when the stimulus is 

 removed? Will the rate be the degree of acceleration observed in 

 experiment (7)? 



(11) Sum up the observations into a concise statement as to the 

 influence of the vagus upon the heart. 



NOTE. Dispatch the rabbit with chloroform. 



X. TO DETERMINE THE INFLUENCE OF THE CARDIAC 



SYMPATHETIC NERVES UPON THE ACTION 



OF THE HEART. 



The appliances should be the same as for the preceding exercise. 



Let the students who work at one table continue the same grouping 

 that was arranged in the preceding exercise, but rotating in the 

 work: Group "a" to operate; group "b" to arrange electric 

 apparatus and stimulate nerve; group "c" to note pulse rate and 

 keep records; group "d" to give anaesthetic. 



The operation should be similar to that of the vagus experi- 

 ment. 



Find the cardiac branch of the cervical sympathetic in the lower 

 part of the neck, where it is in close relation with the carotid artery 

 and the internal jugular vein. The most certain way to recognize 

 it is through its function. Carefully separate out the nerve trunks 

 in the region described; with the glass nerve hook lift up any nerve 

 except the vagus and stimulate moderately. 



7 



