66 PRINCIPLES OF VETERINARY SURGERl' 



those gangrenous conditions that occur in the absence of any 

 direct injury. They are called secondary becaiise their ac- 

 tual cause is always an obturation of blood vessels, more or 

 less remote from the original seat of the gangrene. This 

 form is not as common in animals as the traumatic. Wide- 

 spread thrombosis and arterial sclerosis, the two common 

 causes of occlusion of blood vessels^ are seldom seen in 

 animals. The former is, however, encountered occasionally 

 in the large arteries of both the anterior and the posterior 

 limbs of horses. Thrombosis of the iliac arteries is occasion- 

 ally found, and is capable at any time of producing an ob- 

 struction sufificiently complete to cause sphacelus of the 

 entire limb and death of the patient. The same phenomena 

 are also seen in the anterior limbs. They simulate attacks 

 of lymphangitis in the first stages. Another example of spon- 

 taneous gangrene is the necrosis of molar teeth from athe- 

 romatous degenerations of the radicals of the dental arteries. 

 In these cases the teeth lose their principal blood supply 

 and die as a consequence. 



PATHOLOGICAL ANATOMY.— In every wound 

 taused by bruising there are three kinds of tissues; the dead, 

 the dying, and the viable. In the center of the traumatic fo- 

 cus the dead elements are found attached to, and surrounded 

 by, the dying elements which soon become prey for micro- 

 organisms. The viable elements surrounding the former two, 

 thanks to the reaction of the organism, revive from their 

 weakened state and promptly separate themselves from the 

 dead tissues they encircle. The point of separation soon be- 

 comes distinctly visible and constitutes the "line of demarca- 

 tion" which in due time forms a crevice in the tissues and thus 

 separates the living from the dead. In certain tissues (ten- 

 dons, ligaments, cartilage, etc.) the dead elements remain at- 

 tached to the living, and although the process may be old, no 

 4istinct line of demsircation is formed, Necrotic portion^ of 



