84 EXPERIMENTAL PHYSIOLOGY 



The venous pulse. In a recumbent subject fix a small open 

 receiving tambour (a small thistle funnel will do) at the place in the 

 lower part of the neck where the venous pulse in the jugular is most 

 distinct. The receiving tambour is connected by rubber tubing to a 

 small recording tambour, and the curve is written on paper moved 

 slowly by clockwork. A tracing of the carotid pulse can be ob- 

 tained on the same paper, another tambour being fixed over the 

 artery. A convenient apparatus for taking such tracings is the 

 polygraph of Mackenzie. In this instrument there is a continuous 

 roll of white paper on which the tracings are recorded with ink. 



Fia. 71. DIAGRAM TO SHOW THE LEVER-MECHANISM OP THE DUDGEON SPHTGMOGRAPH. a, SPRING ; 

 6, BUTTON TO BE APPLIED TO THE RADIAL ARTERY ; c, WRITING POINT OP JOINTED LEVER 



ATTACHED TO SPRING ; d, GLASS PLATE OR PAPER ON WHICH THE TRACING IS RECORDED. 



Arterial pressure in man. The pressure of the blood within the 

 human arteries is determined by the sphygmometer, of which many 

 forms are available. All have a circular rubber bag (fig. 72, a) which 

 is enclosed by leather and is placed round the upper arm. The bag is 

 distended with air by a pump (c), the amount of pressure used being 

 recorded either by a mercury manometer (Riva-Rocci) (6) or an aneroid 

 (Hill and Barnard) or by compression of air in a closed tube, using a 

 mercury index (Gr. Oliver). As the distension progresses the manometer 

 shows not only the gradual increase of pressure but also oscillations due 

 to the pulse. These oscillations increase in magnitude up to a certain 

 point. The point around which the oscillations are greatest is the 

 measure of diastolic or average pressure. On further raising the pres- 

 sure the oscillations again become smaller, for the brachial artery is 

 now becoming occluded. When it is completely occluded the pulse 



