CHAPTER II. 

 GENERAL PATHOLOGY. 



CONGESTION, OR HYPER>EMIA. 



Congestion, or hypersemia, is excess of blood in the 

 dilated vessels of any part. It is active or arterial, and me- 

 chanical or venous. 



Active Hypersemia is excess of blood in the arteries of 

 any part, generally accompanied by acceleration of the blood- 

 flow. It is caused by diminished arterial resistance, which 

 may be due to several causes, viz. : 



1. Weakening or paralysing of the coats of the vessels. 



2. Inhibition of the tonic action of the sympathetic on 

 the walls of the vessels, which may occur either directly or 

 reflexly. 



As an example of the direct process may be given the 

 congestion occurring after section of the vaso-motor nerves, 

 in any part of their course from their origin in medulla 

 oblongata, to the spinal or sympathetic plexuses. 



Some drugs also, as nitrite of amyl, tobacco, and alcohol, 

 probably directly paralyse the vaso-tonic nerves. 



The reflex process is due to stimulation of afl'erent nerves. 

 It is seen when food excites the flow of saliva or gastric juice, 



3. Excitation of the vaso-dilator nerves, as, for example, 

 the chorda tympani. 



Mechanical, or Venous Hyperaemia. — In venous hyper- 

 emia the blood-flow is retarded, and the excess of blood is in 

 the veins and capillaries. 



