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A MANUAL OF PHYSIOLOGY 



radial pulse, the jugular pulse, and the cardiac impulse, or of the 

 carotid pulse, the jugular pulse, and the apex-beat, may be taken, 

 and other combinations as well. If no polygraph is available, a 

 drum may be employed, the tracings being all taken with thistle- 

 tubes connected with recording tambours. The levers of the 

 tambours must be arranged to write on the drum in the same 

 vertical straight line, or, without making the adjustment quite exact, 

 vertical lines of reference may be drawn through each curve, with the 

 drum at rest, indicating the relative positions of the writing-points. 

 20. Plethysmographic Tracings. Connect the vessel C (Fig. 47, 

 p. 117) with B, place the arm in it, and adjust the indiarubber band 

 to make a watertight connection. Support C so that the arm rests 

 easily within it, and fill it with water at body temperature. Adjust a 



writing-point, carried by the float 

 A, to write on a drum, and close 

 the upper tubulure of C with a 

 cork. The quantity of blood in 

 the arm is increased with every 

 systole of the left ventricle, 

 diminished in diastole. The float 

 will therefore rise when the ven- 

 tricle contracts, and sink when it 

 relaxes. Or C may be connected 

 by a rubber tube with a record- 

 ing tambour writing on the drum. 



FIG. 91. PLETHYSMOGRAPH (Mosso). 



M, balanced test-tube, in communication with D. When water passes from 

 vessel D to M, or from M to D, M moves down or up, and its movements are re- 

 corded by the writing-point N. M is steadied by the liquid in P, into which it dips. 



No water must get into the tambour, and it is well to insert a 

 piece of glass tubing in the connection between it and the plethys- 

 mograph, so that it may be seen when the water is rising too high. 

 A T-piece with a short piece of rubber tubing on the stem should 

 be inserted in the course of the tube leading to the tambour. All 

 adjustments are made with the T-piece open, and when a tracing is 

 to be taken the short rubber tube is closed by a clip. Arrange a 

 time-marker to write half or quarter seconds (Fig. 76, p. 179). 

 Mosso's arm plethysmograph (Fig. 91) may also be used. 



