MOKTIFICATION. 57 



decomposition being apparent in the part by tbe formation or 

 escape of the gaseous products of putrefaction simultaneously 

 with the appearance of the extravasation, giving the swellings 

 a feeling of crepitation even at the very out-set of the disease. 



Mortification may arise independently of the inflammatory 

 process from defective quantity of blood in a part. This 

 may be due to obstruction of its artery of supply, owing to 

 injury, the formation of a clot within, or pressure constantly 

 maintained upon it. Portions of tissue may also perish when, 

 by injury or by progressive ulceration or absorption, all 

 their minute blood-vessels are destroyed and their supply of 

 blood cut off. I have seen a case where all the gluteal muscles 

 of one side were mortified, from the small arteries having 

 been crushed and destroyed in a railway accident, but whero 

 the larger arteries of supply did not sutfer. The horse lived 

 several days. 



Necrosis may follow the separation of periosteum from the 

 surface of a bone, when it is either stripped off or raised by. 

 effusion, or when there is suppuration beneath it. 



Sometimes a tumour will slough in its centre from defective 

 supply of blood. Again, a part will slough from the application 

 of a strong chemical agent, as corrosive sublimate or arsenious 

 acid. 



Blood defective in quality also produces mortification, without 

 being accompanied by inflammation, and occasionally mere 

 passive congestion of a part may lead to its death ; but this is 

 a rare occurrence. 



The simplest example of mortification of a part, not from 

 deficiency of blood in it, is that from strangulation, as in 

 strangulated hernia. Here, if the strangulation is sudden and 

 complete, the stagnation is equally so, and the death of the 

 part follows very quickly, with but little excess of blood in it. 

 But if the strangulation be less in degree, the veins suffer more 

 from the gradual compression than the arteries do ; the vessels 

 become engorged with blood admitted to them faster than it can 

 leave them, and so, after intense congestion, mortification ensues. 

 (Example — inversion of the uterus.) 



The mortification arising from passive congestion and that 

 from strangulation are said to arise from defect in the flow 

 of the blood. 



