Page 115 - My FlipBook

INFLAMMATION. 113

Again, the paleness of an anemic condition may be due to a
deficiency of the red coloring matter of the red blood corpuscles.
A permanent contraction of the blood vessels may also cause a
paleness of the face, lips, gums and mucous membranes.
The term Ischemia is also employed to denote local poverty of
the blood, a deficiency of the coloring matter (hemoglobin).
The direct cause of hyperemia, and also of ischemia, is a
change of calibre of the blood vessels, namely, dilatation and
contraction. This dilatation and contraction of the blood ves-
sels are due to the elastic and contractile elements of the sheaths
and walls of the arteries and veins, and both the dilatation and
contraction are regulated by the spinal cord, through the medium
of the vaso-motor nerves. It is a common opinion that hyper-
emia cannot exist without the influence of the vaso-motor nerves.
Irritation indicates the condition of a tissue in which there
exists an excess of vital action, on account of the disordered
state of the nerves of the affected part or organ. It is commonly
manifested by such symptoms as increased circulation, warmth
and sensibility, and functional disturbance of a greater or less
degree.
What inflammation is to the vascular system, irritation is to
the nervous system, and the difference between these two con-
ditions is defined bv the explanation that the latter terminates
when the former begins. Irritation is generally excited by the
action of certain stimuli upon organic tissues, by which the
sensibility of such tissues is perverted and the circulation de-
ranged; such pathological conditions when they are not the pre-
cursor of inflammation, soon passing off", and the affected tissue
regaining its normal state when the exciting cause ceases to
operate. Irritation may be direct and indirect— direct when the
irritation manifests itself at the point where the impression to
which it owes its origin is received ; indirect when the irritation,
through sympathy and reflex action, is transmitted to more or
less remote parts or organs. An example of direct irritation mav
be adduced bv friction upon the skin or mucous membrane of
the mouth sufficient to cause redness in the first tissue, and in-
creased coloration in the second ; or indirect irritation, in the