190 STUDIES IN ADVANCED PHYSIOLOGY. 



a condition of things in which a greatly increased peri- 

 pheral resistance in the arteries should arise and produce a 

 hard pulse, and yet the heart itself might force but a small 

 amount of blood into the artery at each beat and so indicate 

 a small pulse at the same time. 



4. Physiological Measurements of the Pulse and Ar- 

 terial Pressure in General. Every one knows that the pres- 

 sure in the arteries may be easily determined by feeling it 

 with the finger. The rhythmic variation in arterial pres- 

 sure which we call the pulse, is commonly examined in this 

 way. But in order to show with much finer detail all the 

 phenomena of arterial pressure, various forms of sensitive 

 instruments have been devised. Possibly the most satis- 

 factory one is the sphygmograph. This consists essentially 

 of a sensitive recording lever placed on the artery in such a 

 way that any increase in the pressure of the artery will raise 

 the lever. The lever itself is then arranged to write on 

 some suitable moving surface and so a curve of pressure is 

 obtained. The philosophy of such an instrument is almost 

 too simple to need further explanation. Every one knows 

 that by putting the finger on the pulse we feel the wall of 

 the artery rise. In fact, this rising we called the pulse. If, 

 now, instead of the finger a sensitive lever be placed on the 

 artery, it is, of course, easy to see that at the moment the 

 pulse wave is under the lever it will lift the lever, and if 

 the distal end of the lever is provided with a recording point 



Fig. 85. SPHYGMOGRAPHIC CITRVKS, i KOM HTM AN KADIAI. AUTKRY. 



a curve will be the result. The sphygmograph possesses 

 the great advantage that it can be used easily and without 

 any injury to the blood vessels, and so is adapted for the 



