The disposition of the tubes in a wound is such that the liquid may readily spread over the whole surface. As it is essential that the antiseptic liquid should be in contact with the tissues themselves, the tubes are not applied over gauze, or over "wicks," but directly to the wound. In fact, a thin compress placed on the surface of granulations might be supposed to be able to distribute the liquid over the whole extent of their surface. Also it might be imagined that "wicks" of absorbent cotton would play a similar part. But nothing of the kind occurs. After a short time, the deeper parts of the absorbent tissue become impregnated with the plasma secreted by the tissues and are then almost impermeable to the liquid. Suppose a thin compress be placed on the surface of the wound and a tube be laid on the compress, liquid injected into the tube slips away over the surface of the wound without sterilising the wound (Fig. 47). Therefore it is absolutely necessary to place the tubes directly in contact with the wound-surface, and then to lay the compresses above them (Fig. 48) in such a manner that the liquid may insinuate itself between them and the surface of the wound.
Fig. 47. - Wound with surface horizontal. Wrong method of placing the tube. The perforated instillation tube is on the surface of the compress.
In the disposal of the tubes it is necessary also to take into account the position of the wound. The flow of liquid being under the influence of gravity, the tubes are arranged differently, according as the wound is situate on the anterior, lateral, or posterior surface of the body. They are placed in such a manner that the liquid may spread itself over the greatest possible extent of the wound (Fig. 49). When the wound is on the anterior surface of the trunk or limbs the application of the tubes is easy. If on the lateral or posterior aspect, prolonged contact between antiseptic and wound surface is more difficult to obtain.
Fig. 48. - Wound with surface horizontal. Right method of placing the tube. Tube in contact with the wound and covered with a gauze compress.
The shape of the wound also plays an important part. A wound possessing but a single opening, and that situated superiorly, can be filled with liquid like a cup, and can be readily sterilised (Fig. 50). If a wound of this type has a second opening at the level of its most dependent part, liquid runs through rapidly and the sterilisation is slower. Gravity plays a very considerable part in the distribution of the liquid and the tubes must be arranged in such a manner as to utilise it.
One or more tubes perforated with minute holes are placed on the wound. If it is situated on the anterior aspect of the body and the bottom of the wound is in the horizontal plane, or nearly so, the liquid can be distributed fairly equally over its surface (Fig. 48). When the surface of the wound is inclined, the tube is laid along the more elevated border (Fig. 49), so that the liquid, carried by gravity, flows over the surface of the tissues. Instead of a simple tube, we may use a ring, formed out of a tube perforated with little holes throughout its middle portion, and whose ends are joined by a Y-shaped cannula (Fig. 51). By means of a thread attached to the two halves of the tube, the loop can be altered to any convenient shape. On the end of a stump, for example, this mode of instillation is useful. Between the raw surface and the base of the flap is placed a loop formed of a rubber tube pierced with multiple hole? whose two extremities are joined by the Y-cannula resting on the skin of the anterior portion of the limb.
Fig. 49. - Wound with surface inclined.
A. Tubes placed the wrong way, along the lower border of the wound.
B. Tubes placed the right way, along the upper border of the wound.
FiG. 50. - Wound with opening superior, so that it can be filled like a cup.
Fig. 51. - Surface wound. The instillation is made by means of a tube perforated in its middle portion, whose ends, fixed to the skin by a strip of adhesive plaster, are joined by a Y-shaped distributor.
Fig. 52. - "Seton" wound, in the interior of which is placed an instillation tube perforated with small holes and which passes through the dressing at its upper part.
The fixation of these tubes is effected by means of gauze compresses soaked in Dakin's solution, which are laid over them. In addition, they are fixed to the skin adjoining the wound by a strip of adhesive plaster. This fixation must be thought out very carefully, because if the tubes slip down to the lowest part of the wound, sterilisation of the upper part will be defective. For, whatever precautions may be taken, the tubes sometimes become displaced. That is why it is advantageous, in the treatment of surface wounds, to replace instillation of liquid by the application of chloramine paste, so soon as sphacelated tissues have been dissolved.