This invasion consists of the fluid portion of the blood—or lymph, and the solid elements called white corpuscles—or leucocytes. These latter remove the cells which have been killed by the injury, and get rid of the blood clot, probably by a process of digestion. When this is effected, the way is paved for the healing, i.e. the formation of the scar.

The naked-eye evidence of all this is to be found in the moisture or exudation on the surface of a wound. As this forms on both surfaces of a wound, the exudation is the first bond of union. The fluid portion of this exudation becomes absorbed, and what remains of it forms the scaffolding on which the scar is built up. The scar consists of new connective tissue cells which have grown into this framework, and multiplied rapidly, causing firm cohesion of the two separate surfaces.

In order that these new cells should be properly nourished they require a sufficient blood supply, and it is found that while their formation is proceeding minute new blood vessels shoot forth from the existing ones, and they grow into the soft newly developing scar tissue. Owing to this fact, free oozing of blood takes place when a healing wound is disturbed.

In the operation of circumcision it is well seen how the circulation of the blood re-acts to injury. When the mucous membrane covering the glans is exposed it looks pale and translucent, because of its scanty blood supply and its thinness. Very soon after it has been torn through, its whole character changes. It becomes engorged with blood, it becomes red and congested it loses its translucency, and at its lacerated edge the process of healing takes place as detailed above.

All scars are at first pink in colour, because more new blood vessels are formed than are required for the permanent nourishment of the part when completely healed. In the course of time these blood vessels shrink and waste away and the scar becomes whiter even than the adjacent skin. This occurs also in the mucous membrane which remains pink for a considerable time. The membrane in fact undergoes the first stage of inflammation as a reaction to the injury it has sustained. The blood vessels become enormously dilated, and its blood supply increased. It presents the best conditions for healing along the edges where it has been torn, but the whole of its outer surface also, which, after reflection becomes opposed to the raw surface between the corona and the cut foreskin inferiorly, becomes united by a similar process to this raw area.

In those cases where the reflection of the mucous membrane has not been perfect a gap will be left between its margin and the cut foreskin, in which healing takes place by granulation or second intention.

The details of this method of healing are similar to the first; the discharge or exudation from the wound takes place in the same manner, but as there are not two surfaces to unite to each other, this exudation simply covers over the wound in the form of a whitish or pale yellow layer of lymph. The fluid discharge should be tolerably clear; if it tends to be thick or milk like in colour it indicates that there has been some accidental contamination of the wound, or that the vital powers necessary for normal healthy repair are below the average. It shows that the inflammatory re-action of the tissues which is the essential requisite for healing has been excessive. In this case not only has the wound been invaded by the white blood cells, which as previously explained, form the groundwork of the new tissue cells; but a further step has taken place. These white cells have been thrown off the surface of the wound and together with the exuded fluid go to form “pus” or matter. All this causes delay in the healing. But eventually the wound becomes filled up by the growth of new connective tissue cells; these continue to multiply until the surface is reached, when the uppermost or epithelial layer of the cut edge of the adjoining skin grows over it, constituting a continuous skin covering.

The defects in the healing process may therefore be briefly summed as being due to some interference with the natural course of physiological repair. They may be comprised under the following heads.

1) Deficient vitality of the infant.