LXII.] RIGID AND ELASTIC TTJBES. 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. 



Fio. 220. Sigmund Mayer's Gas Sphygmoscope, made by Rothe 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.) Miiller'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 make 

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



LESSON LXII. 



RIGID AND ELASTIC TUBES PULSE-WAVE 

 SCHEME OP THE CIRCULATION RHEOMETER. 



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 



