240 THE CIRCULATION OF THE BLOOD 



produce no reflexes of the voluntary muscles, but which will produce marked 

 effects on the heart rate and on the blood pressure. Expose the sciatic nerve, 

 or any other general nerve trunk, cut it, and stimulate the central end for 5 

 seconds. With a proper strength of stimulus a greater effect is produced on 

 the heart and on the blood pressure than by stimulating a small spot of skin. 



4. Cut the right vagus nerve and mark the exact time on the tracing by 

 the signal marker. After 10 to 15 seconds cut the left vagus, marking the 

 time of cutting with the same care on the tracing. As soon as the nerves are 

 cut, the heart-rate will be observed to increase sharply and the blood pressure 

 to rise. The respirations also change in rate and depth, a fact which can 

 be noted on the blood-pressure tracing. Do not disturb the animal or record 

 until stable equilibrium is again reached. 



5. Now lift up the distal end of the divided vagus, and stimu- 

 late it with an electric current of the strength which previously just 

 produced inhibition. Repeat the experiment on the proximal end of the 

 divided vagus. The stimulation of the proximal end of the vagus produces 

 no direct effect on the heart rate when both vagi are cut, but does produce 

 profound changes on the blood pressure owing to vaso-motor effects. 



6. If the rabbit is used, stimulate the depressor nerve, which produces 

 marked fall in blood pressure from reflex effects. 



7. Repeat the stimulation of the central end of the sciatic as described 

 in 3, now that the vagus nerves are cut. The stimulation of this nerve no 

 longer produces changes in the heart-rate, but the blood pressure is influenced 

 as before, showing that the vaso-motor centers are reflexly stimulated. 



8. When you have finished the outline of experiments, give an excess of 

 the anesthetic to kill the animal and continue the record until the animal is 

 dead. The blood pressure will fall rapidly, the heart-rate will become slower 

 but does not cease for a long time. 



Should a clot form in the cannula, put a bulldog forceps on the artery, 

 disconnect the manometer tube, and wash the clot out by a stream of liquid 

 from the pressure bottle. Use care not to allow this fluid to enter the ex- 

 posed wound. 



Represent the results of each individual experiment in the above series 

 in tabulated form which shall show i, the blood pressure and heart rate 

 just before each experiment; 2, during the experiment; and 3, at different 

 times after the experiment until the normal is reached. After the facts are 

 taken from the tracings and arranged in tabular form, make a study of these 

 facts and draw all the conclusions you can concerning the nervous regula- 

 tions of the heart and of the blood pressure. 



20. Arterial Blood Pressure in Man. The arterial blood pressure 

 in man can be measured only indirectly by measuring the pressure which it 

 takes around the arm completely to close the artery. Some form of the 

 Riva-Rocci apparatus, preferably Erlanger's sphygmomanometer, should 



