pressure of 20 cm. of water is a danger limit between compensation
and decompensation of the heart, and a rise above this point will
precede the clinical signs of decompensation.

Hooker also found that there are daily variations of venous pressure
from 10 to 20 cm. of water, with an average of 15 cm., while in
sleep it falls 7 or 8 cm.

It seems probable that there may be a special nervous mechanism of
the veins which may increase the blood pressure in them as
epinephrin solution may cause some constriction.

Wiggers [Footnote: Wiggers C. J.: The Supravascular Venous Pulse in
Man, THE JOURNAL. A.M.A., May 1, 1915, p. 1485.] describes a method
of taking and interpreting the supraclavicular venous pulse. He also
[Footnote: Wiggers C. J.: The Contour of the Normal Arterial Pulse,
THE JOURNAL. A.M.A., April 24, 1915, p. 1380.] carefully describes
the readings and the different phases of normal arterial pulse, and
urges that it should be remembered that "the pulse as palpated or
recorded from any artery is the variation in the arterial volume
produced by the intra-arterial pressure change at that point."

A quick method of estimating the venous pressure by lowering and
raising the arm has long been utilized. The dilatation of the veins
of the back of the hand when the hand is raised should disappear,
and they should practically collapse, in normal conditions, when the
hand is at the level of the apex of the heart. When the venous
pressure is increased, this collapse will not occur until the hand
is above the level of the heart. Oliver [Footnote: Oliver: Quart.
Med Jour., 1907, i, 59.] found that the venous pressure denoted by