CIRCULATION. 143 



medical practitioners. As a means of diagnosis, however, the sphygmogram 

 still leaves much to be desired. The same instrument, applied in immediate 

 succession to different arteries of the same person, gives, as might be expected, 

 pulse-traces of somewhat different forms. The same artery of the same per- 

 son yields to the same instrument at different times different forms of trace, 

 depending upon different physiological states of the circulation. But the same 

 artery yields traces of different form to sphygmographs of different varieties 

 applied to it in immediate succession; and even moderate changes in adjust- 

 ment cause differences in the form of the successive traces which the same 

 instrument obtains from the same artery. It is no wonder, therefore, that 

 great care must be exercised in comparing sphygmographic observations, and 

 in drawing general conclusions from the information which they impart. 



The Details of the Sphygmogram. — Figure 26 is a fair example of 

 the sphygmograms commonly obtained from the healthy human radial pulse. 

 When this trace was taken, the subject's heart was beating from 58 to GO times 



Fig. 26. — Sphygmogram from a normal human radial pulse beating from 58 to 60 times a minute. To be 

 read from left to right (Burdon-Sanderson). 



a minute. The trace records the effects upon the lever of five successive com- 

 plete pulsations of the artery, which all agree in the general character of their 

 details, while differing in minor respects. By the tracing of each pulsation 

 the up-stroke is shown to be sudden, brief, and steady, while the down-stroke 

 is gradual, protracted, and oscillating. The commencing recoil of the arterial 

 wall succeeds its expansion with some suddenness. In many sphygmograms 

 this is exaggerated by the inertia of the instrument. As shown by the t race rep- 

 resented in the figure, and by most such traces, the recoil soon changes from 

 rapid to gradual, and, in the trace, its protracted line becomes wavy, indicating 

 that the slow diminution of calibre varies its rate, or even is interrupted by one 

 or more slight expansions, before it reaches its lowest, and is succeeded by the 

 up-stroke of the next pulsation. In each of the five successive pulsations the 

 traces of which are shown in Figure 26, the line which represents the more 

 gradual portion of the down-stroke of the pulse is made up of three waves, 

 of which the first is the shortest, the last the longest and lowest, and the mid- 

 dle one intermediate in length, but by far the highest. This middle wave is, 

 in fact, the only one of the three to produce which an actual pise of pressure 

 occurs ; in each of the other two, no rise, bul only a diminished rate of decline, 

 is exhibited. The changes of pressure which produce the first aud third of 

 the waves jusl spoken of, in the pulse-trace under consideration, are very 

 obscure in their origin, and are inconstanl in their occurrence, sometimes being 

 more numerous than in the trace shown in Fig. 26, and sometimes failing 

 altogether to appear. 



The Dicrotic Wave. — The oscillation of pressure, however, which pro- 



