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copally, what occurs distal from the compressing armlet, but in 
registering it plethysmographically. 
We take a sufficiently large — comprising the whole forearm and 
the hand of the patient — firmly closed, not leaky plethysmograph. 
A simple tin plethysmograph after the model of Mosso is perfectly 
satisfactory for our purpose. The band of this plethysmograph must 
be made of thick not over-elastie rubber, and wide enough to surround 
a normal upper-arm with a slight tension. Care should be taken 
that the band is long enough to cover the upper-arm to the extent 
of e.g. 10 em. In the front part of the plethysmograph the tube is 
soldered that the rubber tube conducting to the Marry-tambour fits; 
the membrane-displacements of this little tambour are registered in 
the usual way on a revolving drum. The whole plethysmographieal 
apparatus is filled with air. 
If the plethysmograph is applied in this way, the fluctuations of 
volume of the arm, which are caused by pulsation and by respiration 
are recorded on the revolving drum covered by smoked paper. We 
must directly call the attention to the fact that all motions must of 
course be avoided by the patient, as these are also immediately 
followed by fluctuations of volume of the enclosed arm. 
Psychical influences do not at all or hardly disturb our investigations, 
as will appear afterwards. 
Now the armlet that is to compress the arm circularly is applied 
round the rubber band’) of the plethysmograph. This armlet is placed 
in such a way that it surrounds only that part of the plethysmograph- 
band that closely encircles the upper-arm, so that the lower edge 
of the armlet lies at some distance above the part of the plethys- 
mograph-band which bends from the arm to the border of the plethys- 
mograph. In order to be sure of this it is advisable to encircle the 
arm between the border of the plethysmograph and the armlet 
slightly with a rubber tube (part of a stomach-sound e.g.) that is 
fastened in that situation. This has likewise the advantage that the 
part of the plethysmograph-band that has been left uncovered between 
the tin plethysmograph and the compression-armlet is tightly strained 
and by turning aside cannot make the curve miscarry. Fixation 
of the plethysmograph can often prove useful. 
For a compression-armlet we used the armlet with two chambers 
of Wrsauw, connected with a mercury-manometer. The proximal 
chamber of that armlet must receive the so-called “Rand-Pulsationen” 
1) In order to avoid misunderstandings, we shall always call the rubber band 
of the plethysmograph: band, the hollow compression-armlet always: armlet. 
