THE CIRCULATION OF THE BLOOD AND LYMPH 101 



possible to obtain, because the reproduction of it is the most direct. 

 The fact that such a tracing shows a close agreement with the trace 

 of a good sphygmograph properly applied to the corresponding artery 

 on the other side, is a striking proof of the general accuracy of the 

 sphygmographic method for physiological purposes, and enables us to 

 guide ourselves in transferring to man, in whom, of course, tlie sphyg- 

 mograph can alone be used, the information derived from direct 

 manometric observations in animals. 



For the same reason it is unnecessary to discuss the mano- 

 metric tracings, as regards the pulsatory phenomena, in all their 



FIG. 34. ARRANGEMENT FOR TAKING A BLOOD-PRESSURE TRACING. 



M, manometer ; Hg, mercury ; F, float armed with writing-point ; A, thread 

 attached to a wire projecting from the drum and supporting a small weight. The 

 thread keeps the writing-point in contact with the smoked paper on the drum. 

 B is a strong rubber tube connecting the manometer with the artery ; C, a pinch- 

 cock on the rubber tube, which is taken off when a tracing is to be obtained. 



details. It will be sufficient to say that while the form of the 

 blood-pressure pulse-curve varies with the mean blood-pressure, 

 the dicrotic wave is always marked on it, preceded by one or 

 more oscillations falling within the period of the systole, and 

 followed by one or more within the period of the diastole. When 

 the blood-pressure is low, the first or primary elevation is the 



