LXII.] RIGID AND ELASTIC TUBES. 295 



Within fifteen to thirty seconds or thereby it will affect the pulse, lowering 

 the tension, the tracing presenting all the characters of a soft-pulse tracing, 

 with a well-marked dicrotic wave. 



6. Gas Sphygmoscope (fig. 220). 



Connect the inlet tube of the instrument with the gas supply, light the 

 gas-flame (b). Apply the caoutchouc membrane (a) over the radial artery, 

 and observe how the flame rises and falls with each pulse-beat. Take a deep 

 expiration, and observe the dicrotism in the gas-flame. 



FiQ. 220. Sigmund Mayer's Gas Sphygmoscope, made by Bothe of Prague. 



7. Plethysmograph. Use the air-piston recorder of Ellis, and take a 

 plethysmographic tracing of the variations of the volume of a finger. The 

 piston of the recorder must be lubricated with an essential oil, e.g., clove. 



8. Delepine's Gas Sphygmoscope is convenient. (Brit. Med. Jour., July 

 1891.) 



9. Influence of the Respiration on the Pulse. 



(i.) Muller's Experiment. Close the mouth and nostrils and then make 

 a forced prolonged inspiratory effort. Before doing so, feel the pulse, and 

 keep feeling it. Note now the cessation of the pulse-beat. The intra- 

 thoracic vessels are filled with blood, and the distended auricles are unable 

 to contract. 



(ii.) Valsalva's Experiment. Make the experiment as before, but taake 

 a prolonged vigorous expiration. Note fall in pulse-beats. 



LESSON LXII. 



RIGID AND ELASTIC TUBES PULSE-WAVE 

 SCHEME OF THE CIRCULATION -KHEOMETEE. 



1. Rigid and Elastic Tubes. To the vertical stem of a glass 

 U-tube or three-way tube, i cm. in diameter, fix an elastic pump 

 whose opposite end dips into a vessel of water. To the other 



