110 



THE CIRCULATION OF THE BLOOD AND LYMPH 



For the same reason it is unnecessary to discuss the manometric 

 tracings, as regards the pulsatory phenomena, in all their 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 highest of the whole curve (Fig. 42). When 

 the blood-pressure is high, the maximum falls later coinciding with 



one of the secondary 

 systolic waves, bux 

 always preceding the 

 dicrotic wave; and the 

 curve assumes an ana- 

 erotic character. 



That all the secondary 

 oscillations, including the 

 dicrotic wavelet, are cen- 

 trifugal, and not centrip- 

 etal, may be shown, just 

 as in the sphygmographic 

 method, by recording the 

 blood -pressure simultane- 

 ously at two points of the 

 arterial system at differ- 

 ent distances from the 

 heart e.g., in the crural 

 and carotid arteries. The 

 secondary waves are 

 found, by measuring the 

 tracings, to reach the 

 more distal point later 

 than the more central. 



The increase of pres- 

 sure during the systole, 

 as indicated by the height 

 of the primary elevation, 

 is always very large, much 

 larger than it appears in a 

 tracing taken with a mer- 

 cury manometer. In the 

 rabbit this pulsatory variation is one -third to one -fourth of the minimum 

 pressure. In the dog it is still greater, owing to the slower rate of the 

 heart, and often amounts to 50 mm. of mercury, while under favourable 

 conditions (low minimum pressure and slowly - beating heart) the 

 systolic increase of pressure may be actually more than double the 

 minimum (Hiirthle). Pick found also, by means of his spring man- 

 ometer, that the pulsatory variations of blood-pressure were greater 

 than the respiratory variations (p. 289), although in the records of 

 the mercury manometer the reverse appears often to be the case. 

 Landois, too, in the course of experiments in which a divided artery 

 was allowed to spout against a moving surface, and to trace on it a 

 sort of pulse-curve painted in blood (a haemautogram as it is called), 



Fig. 41.- 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 pinchcock on 

 the rubber tube, which is taken off when a tracing 

 is to be obtained. 



