Epithelium, being an epiblastic structure and capable of no other origin save from its kind, can only be supplied from those regions where it has preëxisted. Consequently, ulcers involving the external surface of the body demand a lively epithelial reproduction in order that they may have a normal covering. Epithelial activity sometimes becomes retarded, and is much slower toward the termination of the healing process than at the beginning. The epithelial covering of a healing ulcer is always marked by a delicate whitish or pinkish film, which proceeds from the periphery as well as from any little island of original epithelial structure left. It is well known that after a certain amount of this repair the process sometimes comes to a complete halt, and the various expedients for stimulating and promoting it, as sponge grafting and the different methods of skin grafting, have been devised solely to atone for such sluggishness or inability.
Ulcers of small size, which are more or less exposed to the air in healthy individuals, while also exposed to possibility of infection, nevertheless seem to escape it, owing to the defensive power of the blood serum and the active cells. Such discharge as naturally comes from them, when not excessive, undergoes evaporation until a point is reached where a dry crust or scab is formed. Under this scab granulation proceeds to a point where the pressure of the scab itself, presumably on the level of the surrounding parts, checks its activity, while at the same time epithelial reproduction goes on until it has been completed. Then the scab, being no longer of use, drops off or is detached by slight friction.
Such is granulation tissue: at first a mere trelliswork of temporary and delicate cell structure, traced in a certain amount of intercellular, homogeneous substance, into which the budding vessels project, the whole mounting, nearer and nearer to the surface, day by day, with variable rapidity, diminishing in this regard as the days go by, so that frequently the granulation process comes to an apparent halt before enough new tissue has been formed. While the superficial granulations preserve the characteristics above noted, those deeper down undergo firmer and more complete organization, and the delicate embryonic structures show the same tendency which they do in the growing embryo, by virtue of what Virchow has called metaplasia, to become converted into something higher and more dignified in the tissue scale. These cells do not specialize themselves to the extent of permitting complete repair of organs of special sense. Thus, while a wound in the cornea or retina may be completely healed, it heals by cicatricial tissue, and not by repair of the special structures involved. On the other hand, tissues of more common connective type—fibrous, bone, cartilage, etc.—are capable of regeneration; and it seems to be a part of the privilege of these new granulations to merge themselves into that kind of tissue necessary for filling the gap. Nevertheless the most common result of granulation is its metablastic conversion into fibrous tissue, which has the special characteristic of contractility without elasticity. As a result the scars contract, in consequence of which disfiguring results are sometimes the almost inevitable consequence of healing of extensive losses of substance. In certain instances it is possible by constant effort to overcome the unpleasant effect of this cicatricial contraction. For example, after extensive burn of the anterior part of the arm, the forearm will be gradually and permanently flexed upon the arm by virtue of contraction of the scar in front of the elbow unless some forcible means is practised for maintaining extension of the limb for at least a part of the time. So with many other injuries and the various mechanical or other expedients required to prevent the untoward result. Nowhere are the after-effects more disfiguring or serious than about the face, where the eyelids are drawn out of shape, the contour of the mouth altered, and where, sometimes, there are other extensive manifestations ([Figs. 10] and [11]).
Fig. 10
Cicatricial deformity following burn. (Original.)
Fig. 11
Cicatricial deformity following burn: side view of same case.
Fig. 12