( 1196 ) 
mBp, then at each heart-systole the whole volume of blood will still 
pass under it, and the plethysmograph-curve shows us the changes 
of volume that result from it. 
This will also take place when the mbp (+ Av) has just been reached. 
When, however, the pressure becomes a little higber than that 
mBp-+ Aw, then the artery remains shut during part of the pulsation. 
Instead of the entire volume bcd only ed’ passes under the 
armlet during each heart-systole. A part is constantly arrested by the 
pressure, the volume of blood passing under the armlet becomes 
smaller and from that moment the volume-curve of the plethysmo- 
graph consequently becomes smaller. This moment lies thus a little 
above the mBp + Aw, and the moment before was thembp + Aw. 
Sometimes it can at the same time distinctly be seen that, if the 
pressure reaches just a little above the mBp + Aw, not only the 
pulse-wave of the plethysmograph becomes smaller, but that also a 
diastolic pause can be observed in it. For during the time d’—d" 
no blood is thrown into the arm. Very often, at all events the latter 
part of the pulse-wave has become much more horizontal. This 
occurrence consequently, when it presents itself, furnishes a good 
contro! for the diminution of the pulsation. 
In our curve [ the diastolic pause is not visible but the diminution 
of the pulse at 80 mm. Hg can be distinctly observed. In curve II 
on the contrary the diastolic pause at 85 and especially at 90 mm. Hg 
ean be very well distinguished 
In our example curve | is consequently : 
mBp + Aw = 75 mm. Hg 
Aw (comp. above) was 9 mm. Hg 
Thus mBp = 66 mm. He. 
/ 5 
The phenomena regarding the amplitude of the plethysmographic 
pulse occur, whether the manometer is connected with the armlet 
or whether it is pinched off, and consequently do not depend upon 
the mercury-fluctuations. With the simultaneous. registration of the 
two curves it is, however, peculiar, that the last great pulse-waves 
of the plethysmograph and the greatest oscillations usually show 
themselves at the same pressure, which agrees entirely with our views 
concerning the signification of the greatest oscillations (comp. Chapter I). 
If we closely examine the oscillatory curve, we see how difficult 
it is to find out with certainty the beginning of the oscillations that 
are to indicate the M/Bp. And we see at the same time, how it is 
almost impossible to determine beginning and end of the great oscil- 
lations. And according to our experience this is often the case. We 
