PRACTICAL EXERCISES 



211 



the vago-sympathetic through the sympathetic (pupillo-dilator) fibres 

 that supply the iris. 



(/) Again stimulate the peripheral end of one vagus, or of both at 

 the same time, while a tracing is being taken, and see how long it is 

 possible to keep the heart from beating. Sometimes, but rarely in the 

 dog, inhibition can be kept up so long that the animal dies. 



(g) Close the tracheal cannula so that air can no longer enter the 

 lungs. In a very short time the blood-pressure curve begins to risg. 

 (rise of asphyxia). After some minutes the pressure falls, and finally, 

 when the circulation has stopped completely and the pressure has 

 become equalized throughout the whole vascular system, a residual 

 pressure of only a few mm. (usually about 10 mm. Hg) is indicated. 

 In order to get the true zero pressure, disconnect the arterial cannula 



Fig. 105. Blood-Pressure Tracing from a Dog: Stimulation of Central and Peripheral 

 Ends of Vagus. The other vagus was intact. Stimulation of the peripheral end 

 caused stoppage of the heart and a marked fall of pressure. Stimulation of the 

 central end produced a great rise of pressure, with, perhaps, a slight acceleration 

 of the heart. 



from the manometer, and allow the writing-point to trace a horizontal 

 straight line (line of zero pressure) on the drum (Figs. 84 and 85). 



24. Estimation of the Arterial Blood-Pressure in Man. Use the Riva- 

 Rocci apparatus, as described on p. 113. Begin with the subject in the 

 sitting position. The observer's left hand may be used for palpating 

 the pulse, and the right for working the bulb. Employ the ausculta- 

 tory method as well as palpation, and determine the systolic and dias- 

 tolic pressures. Repeat the observations with the person standing up 

 and lying down. Investigate the effect of muscular exercise on the 

 blood-pressure. 



25. The Influence of the Position of the Body on the Blood-Pressure. 

 -Inject into the rectum of a dog 3 to 4 grin, of chloral hydrate dis- 

 solved in a little water. See chat it does not run out again immediately 



