WOUNDS. 73 



indicates cither a lack of vitality in the system or else external 

 irritation. The latter is usually from germs. 



Development of new blood vessels. — This is from vessels 

 that previously existed in the injured tissue. The growth of 

 new blood vessels and new tissue for union, start together and 

 continue until enough granulation tissue has been developed. 

 After the embryo cells have become fully developed unnecessary 

 vessels begin to disappear. The new vessels start by budding 

 from capillaries near the surface and are always short. These 

 buds project farther and farther and gradually change into 

 threads. These gradually hollow into tubes beginning at the 

 end near the old capillary. It happens frequently that the ends 

 of two neighboring projections meet and unite to form an arch. 

 After this becomes hollowed out we have a capillary loop formed. 

 When this development is complete, then new blood vessels may 

 start out from this one and perhaps develop another arch. The 

 thread-like projections are probably hollowed out by the blood 

 current in the parent vessel. 



Inflammation in wounds is due to foreign material ; for in- 

 stance, dead tissue or foreign bodies, but more commonly by 

 germs which by multiplication give rise to wound infection and 

 inflammation. 



Osseous tissue. — Wounds in bone tissue heal like those in 

 other tissues, the wound surface being covered with granulations. 

 ' The development of new tissue is from the periosteum and from 

 the marrow at the place of injury. At the end of a few weeks, 

 the ends are united by a spongy mass beneath the periosteum and 

 in the medullary canal. This mass gradually becomes organized. 

 This is called a callus and is largely removed later. 



Cartilage has very little power of repair. Loss of cartilage 

 is generally repaired by connective tissue. 



Nerve tissue. ■ — After a nerve is cut, the distal end degen- 

 erates. New axis cylinders come down from the proximal por- 

 tion and grow through or along old sheaths of the distal end. 

 It is doubtful whether primary union ever takes place. Quick- 

 return of sensibility does not necessarily imply restoration of the 

 injured fibers. The proximal axis cylinders enlarge and sepa- 

 rate at the ends. As they grow in length they may extend out 

 into surrounding connective tissue, the proximal end of the nerve 



Vet. Studies — 5. 



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