( 1191 ) 
only cause why the arms swells can be that under the WrBauw 
armlet blood penetrates into the arm. As a proof for the accuracy 
of this reasoning must be admitted the plethysmographic curve 
registered at this pressure, in which a slight pulsation — for the 
first time — can be observed. 
Here we have doubtless before us: the moment of the MBp. That 
is to say that in that MBp of course the factor of the arterial wall 
is included. For the latter will be of use to open the artery. 
At this moment the oscillatory curve shows nothing particular 
that could not be observed at a former pressure. 
Now we wait quietly till the lever of the Marrr-tambour does not 
rise any longer. This takes some time. If at last the lever rises no 
more, we see as a rule that it continues in the position it has 
reached. We shall afterwards revert to exceptions. In case of doubt 
we register a second, third ete. curve at the same pressure. If then 
really the lever. remains at the same height, we know of course 
that the arm does not increase any more in volume, and consequently 
the slight pulse-wave that passes under the compression-armlet is no 
longer able to increase the volume of the arm. 
Then we lower the pressure with e.g. 5 mm. He. (in our case 
to 130 mm.). 
The curve again moves upward and the pulsation becomes more 
distinct. Both occurrences are proofs that the artery opens more 
widely. No change is to be seen as yet in the oscillatory curve. 
Again we wait calmly till the end of the upward move, register 
eventually another curve (comp. the example). 
Now we lower the pressure to 127 mm. Hg and after a few 
moments we see the plethysmographic curve go down rather rapidly. 
What has happened ? 
During the pressures of 135 and 180 mm. He blood continued to 
flow into the arm because the arteries were open and the veins still 
closed. This blood flowed through the arteries, through the capillaries 
towards the veins, and would have lett the arm again, if in the 
veins it had not been arrested by the compression-armlet and kept 
back there. Consequently the volume of blood in the arm increased, 
and the plethysmographic curve rose, and continued to rise of course 
till the pressures distal and proximal of Wysavw’s armlet are equally 
balanced. 
Now we may consider the arteries + capillaries + veins asa system 
of communicating vessels, and certainly so, if we work slowly. As 
long as the pressure in the veins is lower than that in the arteries, 
blood will flow from the arteries into the veins, and consequently 
