186 VETERINARY PATHOLOGY. 



by fibrils continuous with the coagulated extravasate and as 

 the latter is absorbed the scab gradually becomes loosened and 

 finally drops off leaving a shining surface. The regenerated 

 tissue formed in the extravasate is embryonic fibrous tissue the 

 amount of which depends upon the quantity of coagulum. 

 Upon the embryonic tissue thus formed, in surface wounds, 

 epithelization is usually rapid and complete. The scar appears 

 pale pink and is tender until cicatrization takes place and then 

 appears white, dense, firm and hard. Whether the fibrous tis- 

 sue produced in wound healing is substituted later by the nor- 

 mal tissues of the part involved depends upon the generative 

 pi iwer of the tissues destroyed. 



To recapitulate, healing by primary union embraces, coagula- 

 tion uf the hemorrhagic extravasate, agglutination of the wound 

 margins, hyperemia, inflammation, vascularization, fibrous form- 

 ation, disintegration of the hemorrhagic extravasate and in- 

 flammatory exudate, cicatrization, epithelization and substitu- 

 tion. 



Hcalinq bv ijranulatioii. — This is tlie usual mode of wound 

 healing in domestic animals. It dift'ers from the healing by 

 primary union in that there is invariably infection and suppur- 

 ati\e inflammation, degeneration and necrosis preceding regen- 

 eration. This mode of healing takes place in irregular wounds 

 having lacerated margins and in which there is considerable de- 

 struction of tissue and e.xtensive hemorrhage and in wounds 

 tlie margins of which are nnt approximated. The extravasated 

 blood ma)' coagulate in the ^\■ound, especially in subsurface 

 ^vounds, and alsn in surface wounds in which the margins are 

 approximated and retained bv mechanical means, such as su- 

 tures, adhesive tape, etc. In lacerated or gaping surface 

 wounds, as wire cuts, the coagulum becomes detached and 

 drops out leaving the wound margins covered by a thin layer 

 of coagulated serum. Within a short time after the injurs i? 

 inflicted there is extensive leucocytic immigration into the tis- 

 sues bordering the wound. The infective micro-organisms cause 

 destruction and solution of the marginal cells until the tissue re- 

 sistance or local immunity checks their activity. Upon the ex- 

 posed wound surfaces there appears velvet like projections 

 (granulations), which are capillary loops regenerated from ad- 

 jacent vessels. 



Between and intermingled with the granulatior.s. regenera- 

 tion of connective tissue takes place. Constant exposure of the 

 wound insures continued infection which retards the granula- 

 tion more or less, depending upon the extent cif the infection,. 



