OF VETERINARY MEDICINE. 23 



Petechise are small red spots formed by the blood oozing out 

 through the vessel. When a more extensive hemorrhage forms 

 it is called ecchymosis. Hemophilia is an abnormal tendency to 

 bleeding. It is usually hereditary. 



After an excessive hemorrhage, — one that would produce 

 infarction, gangrene is apt to follow. Moderate congestion 

 maintained for any length of time, i. e., indefinitely, will result 

 in hypertrophy. The opposite extreme, anaemia, will produce 

 atrophy of a part. 



The causes of passive congestion are: 



1. ]\Iechanical obstruction. 



2. Diminished cardiac power. 



3. Gravitation. 



4. Altered conditions of the blood. 



5. Defective secretion. 



The last four of these causes we speak of as more compli- 

 cated. The natural result of diminished cardiac power is less 

 force to drive the blood through the vessels. The venous system 

 especially suffers. Passive congestion of the lungs is common. 



Passive congestion by gravitation is seen in horses whose 

 legs stock or swell up. The cause of this is a poor circulation in 

 which the walls of the blood vessels are weak and the veins 

 become dilated, and the blood settles in them by gravitation. 



Altered conditions of the blood are seen especially in black- 

 leg, in which the quarters swell up, forming crackling tumors. 

 When one of these is punctured, bloody water flows out; the 

 blood is tarry from the action of the germs causing the disease. 

 The swollen quarters are passively congested. 



Defective excretions in an animal cause oedematous swellings. 

 In other words, the emunctories are inactive. For instance, a 

 horse's legs swell — he is otherwise in good health — give him 

 a purgative and the oedema will disappear. 



The topical signs of active congestion are as follows: 



1. Redness — Rubor. 



2. Enlargement and swelling of arterioles 



and thickening of their walls — Tu- 

 mor. 



3. Heat — Calor. 



