102 



A MANUAL OF PHYSIOLOGY. 



highest of the whole curve (Fig. 35). When the blood-pressure 

 is high, the maximum falls later, coinciding with one of the 

 secondary systolic waves, but always preceding the dicrotic 

 wave ; and the curve assumes an anacrotic character. 



That aft the secondary oscillations, including the dicrotic wavelet, 

 are centrifugal, and not centripetal, may be shown, just as in the 

 sphygmographic method, by recording the blood-pressure simul- 

 taneously at two points of the arterial system at different 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 pressure 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 mercury 

 manometer. In the rab- 

 bit this pulsatory varia- 

 tion 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 beat- 

 ing heart) the systolic 



FIG. 35.-CURVES OF BLOOD-PRESSURE TAKEN increase of pressure may 

 WITH A SPRING MANOMETER FROM THE be actually more than 

 CAROTID ARTERY OF A DOG (HURTHLE). 



When i was taken the blood-pressure was hign ; 

 2 corresponds to a medium, 3 to a low, and 4 to a 

 very low, blood-pressure ; p is the primary eleva- spring manometer, that 

 tion this and the succeeding elevations between the pulsatory variations 

 p and a are called systolic waves ; the systolic of blood - pressure were 

 waves are followed by a marked elevation d, which greater than the respira- 

 corresponds to the dicrotic wave. tory variations (p. 103), 



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), observed that the rate of escape of the blood was 

 nearly 50 per cent, greater during the systole than during the pause 

 of the heart. The existence of the dicrotic wave on this tracing 

 was long looked on as the best proof that it was not an artificial 

 phenomenon. 



The wave of increased pressure, as it runs along the arterial 

 system, carries with it wherever it arrives an increase of potential 

 energy. But this excess of potential energy is continually being 



double the minimum 



(Hurthle) . Fick found 



v , 



also ' b ^ means of his 



