wall which takes place when the heart retires is denoted by a corre- 

 sponding fall in the tube. The tube is supplied with a graduated 



Fig. I. 



Sphygmoscope. 



scale to denote the rise and fall with exactitude. The glass tube is 

 provided at the top with some contrivance, such as a brass screw 

 and collar, to prevent the egress of the liquid when th'e instrument 

 is not in use, or a bulb with an orifice may be supplied. When 

 employed, the glass tube is left open to permit of the passage of the 

 air to and fro. 



The sphygmoscope is mounted upon a stand. The chamber and 

 tube are fitted to a horizontal arm, which is made to move up and 

 down so as to carry the instrument to the desired height. The base 

 is so made as to secure the requisite immobility. 



The glass tube is a foot or more long, and the round bore is about 

 the one-eighth part of an inch. If the bore be much larger, the 

 movement will be inconsiderable ; if much less, capillary attraction 

 will interfere and prevent free motion. 



When the instrument is to be employed, mounted upon its stand, 

 it is placed upon a firm table with the chamber projecting beyond it. 

 The person whose heart is to be examined is seated upon a firm 

 chair, with his chest erect and free from motion. The protruding 

 india-rubber wall of the chamber or chest-piece is delicately made to 

 touch the fifth intercostal space so as to receive the blow of the apex 



c 2 



