pain.

#Modifications of the Process of Repair.#--The process of repair by
primary union, above described, is to be looked upon as the type of all
reparative processes, such modifications as are met with depending
merely upon incidental differences in the conditions present, such as
loss of tissue, infection by micro-organisms, etc.

_Repair after Loss or Destruction of Tissue._--When the edges of a wound
cannot be approximated either because tissue has been lost, for example
in excising a tumour or because a drainage tube or gauze packing has
been necessary, a greater amount of granulation tissue is required to
fill the gap, but the process is essentially the same as in the ideal
method of repair.

The raw surface is first covered by a layer of coagulated blood and
fibrin. An extensive new formation of capillary loops and fibroblasts
takes place towards the free surface, and goes on until the gap is
filled by a fine velvet-like mass of granulation tissue. This
granulation tissue is gradually replaced by young cicatricial tissue,
and the surface is covered by the ingrowth of epithelium from the edges.

This modification of the reparative process can be best studied
clinically in a recent wound which has been packed with gauze. When the
plug is introduced, the walls of the cavity consist of raw tissue with
numerous oozing blood vessels. On removing the packing on the fifth or
sixth day, the surface is found to be covered with minute, red,
papillary granulations, which are beginning to fill up the cavity. At
the edges the epithelium has proliferated and is covering over the newly
formed granulation tissue. As lymph and leucocytes escape from the
exposed surface there is a certain amount of serous or sero-purulent
discharge. On examining the wound at intervals of a few days, it is
found that the granulation tissue gradually increases in amount till the
gap is completely filled up, and that coincidently the epithelium
spreads in and covers over its surface. In course of time the epithelium
thickens, and as the granulation tissue is slowly replaced by young
cicatricial tissue, which has a peculiar tendency to contract and so to
obliterate the blood vessels in it, the scar that is left becomes
smooth, pale, and depressed. This method of healing is sometimes spoken
of as "healing by granulation"--although, as we have seen, it is by
granulation that all repair takes place.

_Healing by Union of two Granulating Surfaces._-