Chap, xxi.] THE SPHYGMOPHONE. 235 



The gas spliygino scope is a little metal cham- 

 ber, having a tube projecting from the top and one 

 projecting at one side, and having the bottom, 

 formed of a delicate membrane. Gas is led by the 

 side tube into the chamber, and out by the top tube. 

 From its exit pipe the gas is led to a glass tube, bent 

 upwards, and drawn to a fine point, so that when the 

 gas is lit, a fine pointed flame is produced. The little 

 chamber is then placed with its membrane over an 

 artery. The movements of the pulse cause variations 

 of pressure in the gas, and these are signified by regu- 

 lar up and down movements of the flame. 



The spliyganoplione is an adaptation of the 

 gas sphygmoscope, after the method used for obtaining 

 a sound from the hydrogen flame. A long glass 

 tube of sufficient diameter is brought down over the 

 gas jet, which is permitted to burn inside the wider 

 tube. The long tube is brought down till a pecu- 

 liar note is produced by the vibrations of the flame. 

 If, now, the gas chamber be placed over the pulse, 

 something like beats will be produced in the tone, due 

 to the variation of the pulse. 



In a similar way A PULSE ALARUM might be con- 

 structed by means of a very small chamber, with 

 movable bottom, and glass tube projecting upwards. 

 The chamber is filled with mercury, which is also 

 allowed to rise some way in the tube. Plunged in 

 the mercury in the tube is a copper wire, forming 

 part of the circuit of an electric bell. A second wire, 

 completing the circuit, is passed down the tube, just 

 so far that when the mercury rises with the pulse 

 wave contact is made, and when the mercury falls 

 with the vessel's recoil, contact is broken. The bell 

 will ring each time contact is made, and will thus 

 indicate the rapidity of the pulse waves. 



Before leaving this subject of the mechanics of the 

 circulation it may not be out of place to describe a 



