236 EXPERIMENTAL PHYSIOLOGY. 



the milled head. Smoke the band of paper, insert it 

 between the rollers, and take a tracing. 



4. Ludwig's Improved Sphygmograph. Use this instrument 

 (Fig. 109a). It is not unlike a Dudgeon's Sphygmograph, 

 but there is a frame adapted to the arm, and an arrangement 

 for keeping the arm steady while the hand grasps a handle for 

 the purpose. 



5. Action of Amyl Nitrite. 



(.) With the Sphygmograph adjusted, place two drops 

 not more of amyl nitrite on a handkerchief, and inhale the 

 vapour. 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. The Gas Sphygmoscope (Fig. 110). 



(a.) Connect the inlet tube of the instrument with the 

 gas supply, light the gas-flame (6). 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. 



Fig. 110. 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 

 a volatile oil e.g., clove. 



