VI 



SOURCE OF GRANULATION TISSUE 



689 



fibroblasts. Furthermore, in contrast to cultures of dermal and loose connective 

 tissue, the cells have a tendency to spread and infiltrate the medium, forming new 

 germinal centers apart from the original explant. Wound healing in cultured 

 explants is retarded in l^oth rate and degree (Ruth, 191 1 ; Bentley, 1936) and no 

 true granulation tissue is formed. Under such conditions the vascular pool is not 

 available to the wound, but in view of numerous other environmental changes 



that occur in vitro it is diflicult to 

 evaluate such indirect evidence. 

 (b) There seems to be little 

 question that a majority of cells 

 which ultimately form granula- 

 tion tissue arise from areas immedi- 

 ately adjacent to the wound. The 

 initial stage of fibrin clot forma- 

 tion with its contained red blood 

 cells, leukocytes, and mononuclear 

 cells persists for only a short time, 

 following which leukocytes rap- 

 idly degenerate and actual pro- 

 liferation of mesenchymal ele- 

 ments begins. In vivo observation 

 of wounds by means of transparent 

 chambers have yielded consider- 

 able information concerning the 

 manner in which granulation tis- 

 sue invades the initial clot. ^ Three 

 distinct cell types are known to 

 play an important role in this proc- 

 ess : a) endothelial cells, b) reticulo- 

 endothelial cells, c) fibroblasts. 



Capillary formation is essential 

 for the production of granulation 

 tissue, clinical evidence for which can be gained from observation of scalp wounds. 

 If the outer table of the skull is chiseled off, multiple bleeding points are exposed. 

 If the surface is kept moist and dressed frequently, it will form a profuse layer of 

 granulation tissue which can be derived only from capillaries and their supporting 

 structures or from blood elements. In transparent chambers, undamaged vessels ad- 

 jacent to the defect can be seen to sprout solid endothelial buds. These buds move in 

 the direction of the defect and ultimately develop a lumen. The advanced portion of 

 the bud is freely permeable to erythrocytes and the latter form a hemorrhagic 

 zone ahead of the capillaries. As pointed out by Van den Brenk (1956), mitosis 

 is seldom seen in these buds, which indicates that either cell division occurs 

 rapidly or that vascular penetration, like epithelialization, is chiefly a phenomenon 

 of migration. There is no evidence to support the contention that capillaries 



Fig. 1 1. Third-degree burn of the skull showing the 

 exposed outer table. 



^ For a thorough review of this subject, see Williams (1954), 



Literature p. 703 



