34 Veterinary Mediciyie. 



cutting of a sympathetic trunk, that of the abdomen, for example, 

 which leads to active congestion of the abdominal viscera, or the 

 section of the cervical sympathetic which leads to watering of the 

 eye, sweating, congestion, and scabbing on the corresponding 

 half of the face. 3d, by reflex irritation through the sensory 

 nerves, as in congestion through friction, heat or cold to the skin, 

 or that resulting from excessive use of an organ such as the 

 mammary gland. 4th, by causes acting directly through the 

 brain as in emotional blushing or the facial congestion of violent 

 rage. 



Physiologically we see the operation of this nervous control in 

 the congestion of the gums during dentition, of the .salivary glands 

 during mastication, of the stomach and bowels during dige.stion, 

 of the womb during gestation, of the mammae at parturition, and 

 of erectile organs in copulation. 



Medicinal agents act in the same way, opium or alcohol pro- 

 ducing active dilatation, and belladonna and ergot causing active 

 contraction of the arterial walls. 



Bacteridian poisons act in the same way, tuberculin and a num- 

 ber of others causing active dilatation. 



The obstruction of one artery by thrombus, tumor, or ligature, 

 causes increased tension in the collateral branches coming off just 

 above and an active congestion in the parts to which these are 

 distributed. While this is directly due to increased local pres- 

 sure, it is also an instance of the lack of balance between the blood 

 pressure and the resistance of the vascular walls. In this case 

 there is increase of pressure, in the other a diminished resistance. 



If there is a superficial anaemia, as from cold or chill, there is of 

 necessity, an internal hyperaemia. This contributes to the pro- 

 duction of internal congestions and inflammations, though the 

 seat of election of such inflammation is usually determined by the 

 nervous sympathy between the part chilled and the deeper organ 

 affected. 



Another cause of congestion is the lessening of pressure by the 

 parts surrounding the vessel. Thus in cupping, there is prompt 

 cutaneous congestion, and a similar result occurs in pericardium, 

 pleura, or peritoneum on the withdrawal of the liquid of hydro- 

 pericardium, hydro-thorax or ascites. 



Another cause of congestion is found in hypertrophy of the 



