rise in the systolic pressure after even slight exercise, and those
with marked cardiac insufficiency have even a lowering of blood
pressure from the ordinary level. They all have increase in pulse
rate. He quotes several authorities as showing that during muscle
work the carbon dioxid of the blood is increased in amount, which,
stimulating the nervous centers controlling the suprarenal glands,
increases the epinephrin content of the blood. The consequence is
contraction of the splanchnic blood vessels, with a rise in general
blood pressure. Also, the quickened action of the heart increases
the blood pressure. After a rest from the exercise, the extra amount
of carbon dioxid is eliminated from the blood, the suprarenal glands
decrease their activity, and the blood pressure falls.

Nicolai and Zuntz [Footnote: Nicolai anal Zuntz: Berl. klin.
Wehnschr., May 4, 1914, p. 821.] have shown that with the first
strain of heavy work the heart increases in size, but it soon
becomes normal, or even smaller, as it more strenuously contracts,
and the cavities of the heart will be completely emptied at each
systole. If the work is too heavy, and the systolic blood pressure
is rapidly increased, it may become so great as to prevent the left
ventricle from completely evacuating its content. The heart then
increases in size and may sooner or later become strained; if this
strain is severe, an acute dilatation may of course occur, even in
an otherwise well person. Such instances are not infrequent. A heart
which is already enlarged or slightly dilated and insufficient,
under the stress of muscular labor will more slowly increase its
forcefulness, and we have the delayed rise in systolic pressure.

Barringer concludes that: