PRINCIPLES OF VETERINARY SURGERY 63 



ease or injury will more readily become necrotic than an ab- 

 solutely healthy tissue ; and an animal weakened from dis- 

 ease, over-work or bad hygiene is much more liable to de- 

 velop gangrene from lesions that would otherwise prove less 

 serious. 



Etiologically, gangrene may be divided into primary, or 

 traumatic and secondary or spontaneous, 



I. Primary or traumatic gangrene is caused by direct 

 injury to, or disease of, a given tissue. The injuries may be 

 mechanical, chemical or thermic. These influences either kill 

 the tissues at a single blow, injure them beyond repair, or 

 else reduce their vitality so as to make them easy prey for in- 

 truding micro-organisms. Various forms of mechanical vio- 

 lence are capable of producing injury severe enough to cause 

 immediate or subsequent death of the wounded part; in fact, 

 all contusions of more than nominal severity, cause the death 

 of a portion of the bruised tissue. These include kicks, blows, 

 treads, lacerations, etc., which cause death by crushing, dis- 

 organizing and separating the anatomical elements, and by 

 creating favorable food for microbian growth. Chemical 

 substances, — caustics, — coagulate the protoplasm and like 

 the contusion, either entirely kill the tissue at once or else 

 injure it beyond repair. Burns and scalds afifect the tissues 

 in much the same manner, while freezing produces gangrene 

 by arresting the flow of blood and causing general systemic 

 enfeeblement. 



Gangrenous dermatitis (mud-fever) affecting the legs of 

 horses is a striking example of gangrene resulting from a 

 trivial injury, becoming infected with virulent micro-organ- 

 isms. It is a true mycotic gangrene. The- skin becomes 

 literally choked with micro-organisms and dies as the result 

 of the strangulation of its capillaries and the dissolving in- 

 fluence of microbian products. A trivial injury badly infected 

 is capable of producing a gangrene even more serious than if 



