eventually become grouped in bundles, constituting fully formed white
fibrous tissue. In its growth it gradually obliterates the capillaries,
until at the end of two, three, or four weeks both vessels and cells
have almost entirely disappeared, and the original wound is occupied by
cicatricial tissue. In course of time this tissue becomes consolidated,
and the cicatrix undergoes a certain amount of contraction--_cicatricial
contraction_.

_Healing of Epidermis._--While these changes are taking place in the
deeper parts of the wound, the surface is being covered over by
_epidermis_ growing in from the margins. Within twelve hours the cells
of the rete Malpighii close to the cut edge begin to sprout on to the
surface of the wound, and by their proliferation gradually cover the
granulations with a thin pink pellicle. As the epithelium increases in
thickness it assumes a bluish hue and eventually the cells become
cornified and the epithelium assumes a greyish-white colour.

_Clinical Aspects._--So long as the process of repair is not complicated
by infection with micro-organisms, there is no interference with the
general health of the patient. The temperature remains normal; the
circulatory, gastro-intestinal, nervous, and other functions are
undisturbed; locally, the part is cool, of natural colour and free from
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._--In gaping wounds union
is sometimes obtained by bringing the two surfaces into apposition after
each has become covered with healthy granulations. The exudate on the
surfaces causes them to adhere, capillary loops pass from one to the
other, and their final fusion takes place by the further development of
granulation and cicatricial tissue.

_Reunion of Parts entirely Separated from the Body._--Small portions of
tissue, such as the end of a finger, the tip of the nose or a portion of
the external ear, accidentally separated from the body, if accurately
replaced and fixed in position, occasionally adhere by primary union.

In the course of operations also, portions of skin, fascia, or bone, or
even a complete joint may be transplanted, and unite by primary union.

_Healing under a Scab._--When a small superficial wound is exposed to
the air, the blood and serum exuded on its surface may dry and form a
hard crust or _scab_, which serves to protect the surface from external
irritation in the same way as would a dry pad of sterilised gauze. Under
this scab the formation of granulation tissue, its transformation into
cicatricial tissue, and the growth of epithelium on the surface, go on
until in the course of time the crust separates, leaving a scar.

_Healing by Blood-clot._--In subcutaneous wounds, for example tenotomy,
in amputation wounds, and in wounds made in excising tumours or in
operating upon bones, the space left between the divided tissues becomes
filled with blood-clot, which acts as a temporary scaffolding in which
granulation tissue is built up. Capillary loops grow into the coagulum,
and migrated leucocytes from the adjacent blood vessels destroy the red
corpuscles, and are in turn disposed of by the developing fibroblasts,
which by their growth and proliferation fill up the gap with young
connective tissue. It will be evident that this process only differs
from healing by primary union in the _amount_ of blood-clot that is
present.

_Presence of a Foreign Body._--When an aseptic foreign body is present