APPENDIX. 311 



on a suitable operating board, and a cannula placed in the trachea, thus 

 facilitating the administration of ether, which may be necessary in 

 order to abolish all reflexes. A cannula is inserted in the carotid artery 

 and is attached to the recording apparatus, as described on p 000 (see 

 Fig. 21). When all is ready, the drum is started at a slow speed, and the 

 clamp on the artery removed. A tracing of the blood pressure showing 

 the individual heart beats is made on the drum. With every respira- 

 tion, a small change in the pressure is recorded, the pressure being 

 highest during the latter part of inspiration, and falling during 

 expiration. 



B. To Show the Effect of Varying the Pumping Action of the Heart on 



the Blood Pressure. 



The vagus nerves on either side of the neck are found in the sheath 

 with the carotid artery. A thread is passed loosely about both. A short 

 bit of normal tracing is made on a slow drum, then one vagus is cut 

 and a minute later the opposite one is severed. This is followed by a 

 marked increase in the blood pressure and a quickening in the heart 

 beat. The peripheral end of the vagus on one side is then stimulated 

 by means of electrodes attached to an induction coil giving a tetaniz- 

 ing current. The heart is slowed or ceases to beat for a short period 

 and the blood pressure falls to zero. The heart soon beats again, for 

 the vagus is not able to inhibit its action for a long period of time 

 (p. 000). This experiment shows that the pumping action of the heart 

 is necessary to maintain the blood pressure, and that an increased 

 rate of the heart is accompanied with an increase in blood pressure, 

 other things remaining equal. 



C. To Show the Effect of Varying the Peripheral Resistance on the 



Blood Pressure. 



The. stimulation of the splanchnic nerve. 



The left splanchnic nerve is exposed just above the supra-renal cap- 

 sule, and is laid on a pair of electrodes. While taking a normal tracing 

 stimulate the nerve with a weak electrical current and then with 

 stronger currents. A great increase in the blood pressure is obtained, 

 due to the constriction of the vessels of the viscera and the increase 

 in the resistance which they offer to the flow of blood through them 

 (see p. 000). 



D. To Show the Actual Changes in the Kidney Vessels Accompanying 



the Stimulation of the Splanchnic Nerve. 



The left kidney is incased in a plethysmograph, which is connected 

 with rubber tubing to a tambour equipped with a writing style. A.n 



