48 PRINCIPLES OP VETEBINAKY SUEGEET 



necrosis ; (3) secondary septic necrosis following tlie entrance 

 of infectious agents. 



4. Contusion of the fourth degree. Complete pulpifica- 

 tiou of the contused parts. 

 Describe the microscopical changes in bruised tissues. 



Slight contusions exhibit a tearing of the smallest blood 

 vessels and their accompanying delicate loose connective 

 tissue. In more serious bruises the intercellular substance is 

 ruptured, pushing the cells apart. Destruction of the cells 

 themselves, even in most serious contusions, is seldom 

 observed. 



How does the microscopic study of contused tissues prove that 

 the contusion per se cannot be looked upon as the direct 

 cause of necrosis ? 

 It shows that while the intercellular substance may be 



torn, the cells themselves remain intact, preserving their 



vitality, thus power of regeneration. 



How do contusions terminate 9 



Termination differs according to their extent, location, 

 degree, presence or absence of infection. They terminate by 

 (1) resorption, (3) organization, (3) necrosis. 



Describe the process of resorption. 



Occurs in contusions of the first degree. The extrava- 

 sation is taken up by the lymph vessels. First the coagulum 

 squeezes out the serum which enters the lymph vessels; next, 

 the coagulated fibrin becomes liquefied and is absorbed; then 

 the white blood cells and finally the red ones disintegrate and 

 enter the circulation. 



Describe the process of organization. 



Seen in more extensive extravasations, especially hema- 



