2-20 



METHODS OF RECORDING PULSE. [Book i. 



which is only a modification of it (see § 113), can be applied to an artery 

 by a cannula in the ordinary way. 



The " sphygmoscope " consists of a small elastic bag, the end of an 

 india rubber finger, for instance, fitted on to a conical cork, through 

 which passes a tube opening into the bag, and connected by a cannula 

 with the artery ; both bag and tube are, before being connected with 

 the artery, filled with fluid of a nature to hinder clotting. The bag, by 

 means of the conical cork, is firmly fitted into the end of a small glass 

 tube, the cavity of which filled with air is connected with a recording air 

 tambour. The changes of pressure within the artery are transmitted to 

 the elastic bag, and through this to the air of the glass tube and so to the 

 recording tambour. 



The tambour-sphygmoscope of Hurthle is a combination of the 

 membrane-manometer with a tambour. The membrane of the manometer 

 works not directly on a lever, but on a recording air tambour, the move- 

 ments of which are recorded in the usual way. 



In the sphygmotonometer of Roy, the artery is, by means of a 

 cannula, and rigid tube filled with fluid, connected with a cylinder in 

 which a light piston works by means of a delicate membrane. 



Fig. 56. Fick's Spring Manometer. 



The flattened tube in the form of a hoop is firmly fixed at one end, while the 

 other free end is attached to a lever. The interior of the tube, filled with spirit, is 

 brought, by means of a tube containing sodium carbonate solution, into connection 

 with an artery, in much the same way as in the case of the mercury manometer. 

 The increase 'of pressure in the artery being transmitted to the hollow hoop, tends 

 to straighten it, and correspondingly moves the attached lever. 



