HYPERiEMIA OR CONGESTION.
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SECTION II.
In the present section it is proposed to consider certain morbid conditions which are included under general pathology, of which it is most desirable to have a comprehensive knowledge before studying- them in connection with special organs or tissues.
Chapter I.
HYPERAEMIA OR CONGESTION.
Hyper^jilv or congestion signifies the presence of an excessive amount of blood in a part. According to its cause and to the vessels in which the accumulation chiefly occurs, the hyperaamia is said to be : — i. Active or Arterial: 2. Meelianical or Venous; 3. Passive or Capillary. Each of these forms requires separate con- sideration.
I. Active or Arterial.— Determination of blood.— In this form the arteries are chiefly implicated, being dilated, while there is an increased afflux of blood through them, though usually too much blood passes out by the veins as well, and the circulation is accele- rated.
tEtiology. — I. Paralysis of the muscular coat of the arteries is the usual cause of active congestion, in consequence of which they yield to the normal pressure of the blood. It is well known that this coat is under the control of nerve fibres which pass from the spinal cord through the sympathetic, and these exercise an import- ant influence on certain pathological processes, including active congestion. The paralysis may be produced : — a. By direct lesion of the spinal cord in experiments, or as the result of injury or disease, b. By injury to the sympathetic trunk, of which the con- gesuon resulting from the pressure of an aneurism upon the sym- pathetic in the neck is an example, c. By reflex irritation through the sensory nerves, such as the congestion following the applica- tion of a mustard poultice, heat, or cold to the skin; or that result- ing from the excessive use or increased activity of an organ, such as the eye or mammary gland. Under the same category may be mentioned the congestion which often attends severe neuralgia. Probably many cases of congestion of internal organs originate in this way, and it may be the first step towards inflammation. d. By causes acting through the brain, which may be illustrated by emotional blushing, and by the effects of some poisons.
2, The rapid withdrawal of external support Irom arteries may cause them to be dilated, and thus lead to active congestion. This is seen in the effects following the application of a cupping-glass to the surface, by which the pressure of the atmosphere is removed,
3. The internal pressure on the vessels may be increased, either from an augmented force on the part of the heart, which princi-
