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Wounds and Their Treatment

WOUNDS AND THEIR TREATMENT.

General Remarks. - In popular language a wound may be defined as a breach of the skin or flesh due to a hurt or injury. In scientific language a wound may be described as a forcible solution of continuity or division of the tissues of any part of the body, caused by a mechanical agent or external violence. Wounds vary as regards their gravity and results, these depend ing on the extent of the injury, the structures involved, the sequelae and complications which may ensue, the vital resistance of the animal, and last but not least, the treatment adopted.

In veterinary practice the subject of wounds and their treatment is one of vast importance, and this branch of surgery forms a large pro portion of the daily work of the veterinarian. Not only has he to adopt measures which are calculated to overcome the immediate and remote effects of wounds, but he must also devote attention to the economical aspect of the subject in the case of horses, so that the treat ment he carries out may render the animals fit for work in the shortest time possible, and reduce to a minimum the chances of blemish. The owners of animals can accomplish much in this direction by calling in professional assistance early, and by avoiding irrational measures prior to seeking skilled advice. Atten tion to the surroundings of the patients and a practical knowledge of cleanliness in dealing with wounds are details which play an im portant part in connection with the results of treatment, which should be fully recognized in first-aid instruction on the subject.

In common with all medical and surgical conditions associated with animals, the treat ment of wounds from the amateur or popular point of view is surrounded by many fads and fallacies. Hence, in dealing with the subject it is essential to discuss the erroneous ideas that are usually held by owners of animals with regard to the healing of wounds, as well as the measures to be adopted in order to assist the natural process of repair.

The first point which merits careful attention is that the healing of wounds is brought about by a natural method of repair. This process takes place independent of surgical interference, and although by adopting certain measures it is possible to assist nature in the work of repair, it is important to remember that if too strong antiseptics or irritants of any kind be applied, healing is retarded instead of being expedited. A common error is to imagine that frequent dressing of wounds is necessary, and to over look the fact that meddlesome interference is harmful in every branch of surgical work. Lack of knowledge in this direction was respon sible for the irrational treatment of wounds practised in former times, and accounts for the erroneous views on the subject held in the present day by many owners of animals.

The next point refers to the prevalent idea that special virtues reside in certain agents employed as wound dressings. The truth is that, provided efficient drainage exists or is assured, the selection of an antiseptic agent is very often a matter of choice provided it does not cause irritation of the tissues. In the absence of proper drainage, the most active antiseptics will fail to bring about desired results.

Experimental studies devoted to the healing of wounds, combined with clinical observation, have led to considerable modification in the views held with regard to the mode of applying antiseptics. It has been shown that such agents, if employed in too strong solutions, cause irritation of the tissues and interfere with the natural process of healing.

In order to gain an accurate idea of the influence for good which the surgeon can exert on the healing of a wound, and in the preven tion of serious complications arising from septic infection, it will be necessary to consider the question of natural repair in an aseptic wound, and then to ascertain the effects produced by the entrance of pathogenic micro-organisms.

If it were possible to exclude micro-organisms from wounds, healing would take place by the natural process of repair. Even in cases of lacerated or punctured wounds, complications would rarely occur, as infection is mainly responsible for the protracted course or serious results which often characterize such injuries.

Unfortunately in veterinary practice, except in the case of operations carried out under aseptic (germ-free) conditions, infection to a varying extent occurs in wounds, and what is known as"healing by first intention"is the exception rather than the rule. It may be taken for granted that accidental wounds are more or less septic prior to coming under the care of the surgeon, micro-organisms having gained entrance either at the time of the acci dent or subsequently through carelessness on the part of the owner of the animal or the attendant.

Technically the term"septic"as applied to wounds means that micro - organisms have gained entrance to the part, and includes infec tion from any source. Thus a wound in which suppuration occurs is, strictly speaking, septic or infected. In popular language, however, the term"septic"is usually reserved to describe wounds in which a more serious form of infec tion has occurred, the discharges being fcetid, and the surrounding tissues being involved and invaded by virulent micro-organisms, while not uncommonly there is a tendency for general septievemia (blood poisoning) to supervene.

As will be pointed out later, the occurrence of suppuration is very common during the heal ing process of wounds in animals, owing to the fact that it is very difficult to prevent the entrance of pus - producing micro-organisms, either in the case of operation wounds or in those resulting from accidental causes. The surroundings of animals and the lack of trained attendants to carry out the after - treatment are factors which are largely responsible for the occurrence of wound suppuration. In human surgery, owing to favourable surroundings and the facilities for carrying out aseptic technique and after-treatment, it is the rule for operation wounds to heal without pus formation, first intention."Even in the case of infected accidental wounds in man it is now possible, by adopting special technique, to render them aseptic.

A short reference to the circumstances under which wounds occur in animals will assist in elucidating our subject.

(1) Operation Wounds. - These may be of the type known as incised wounds (see p. 568), or they may involve the loss of tissue, as exempli fied by wounds remaining after the removal of tumours, in which case a considerable cavity results, which gradually becomes filled by granu lations. In modern veterinary surgery every precaution is taken to prevent infection both at the time of operation and subsequently, but owing to the faulty surroundings of the patient suppuration very frequently occurs during the process of healing.

(2) Accidental Wounds. - These form a large proportion of wound cases in veterinary practice, and they occur under a variety of conditions. The nature of accidental wounds varies from a trivial skin cut to deep and extensive lacera tion of the tissues with injury to important structures such as blood-vessels and nerves, and followed by serious complications which may endanger the life of the patient. In certain regions of the animal punctured wounds, although apparently insignificant on casual in spection, are often followed by serious con sequences. Such cases are exemplified by wounds penetrating a joint or involving tendons, and the unfortunate sequeloe depend on the effects of micro-organisms which gain entrance to the part rather than on the mechanical injury inflicted. Accidental wounds may be caused by one horse kicking another, the catkin of the shoe being capable of producing a very serious injury in certain regions.

Shaft wounds sustained during collisions often prove fatal owing to penetration of the chest or abdominal cavity, or from causing rupture of a large artery in a region where it is impossible to carry out ligation of the vessel.

Barb-wire is responsible for many cases of serious wounding of horses at pasture. Ex tensive and serious wounds in the horse are not uncommon as the result of being"horned"by a cow grazing in the same field. Again, horses when at pasture may take fright and in their wild career may come into violent contact with various obstacles capable of inflicting severe injury on any part of the body. A familiar example of a punctured wound which may be followed by serious consequences is that produced by a"gathered nail"in the horse's foot.

In sporting districts wounds in hunters are of very frequent occurrence, especially in coun tries where stone walls and banks abound, as in Ireland. Under these conditions the most common injuries are punctured or lacerated wounds of the knee, hock, fetlock, and coronet, arising from contact with sharp stones or from penetration by a pointed stump of gorse. Other wounds incidental to hunting comprise open joints, a severe"over-reach,"cuts due to com ing into contact with wire, and punctures from thorns (Black thorn). The veterinary surgeon in a hunting district has extensive experience of the above types of wounds, and not infre quently the greatest discrimination and skill are necessary in order to carry out treatment calculated to render the animals fit for work in as short a time as possible, and to prevent the occurrence of permanent blemishes. Trained hunters being valuable animals, it follows that the most approved methods of surgical pro cedure can be adopted in connection with the treatment of wounds without reference to the question of expense. Moreover, the extra trouble taken is amply repaid by the results obtained.

Repair of Wounds.

- In order correctly to appreciate the principles which should guide us in the treatment of wounds it is necessary to be acquainted with the natural mode of repair. In surgical as well as in medical conditions, natural powers of recovery exist, and it is lack of appreciation of this fact which is responsible for the irrational treatment of wounds so fre quently carried out by owners of animals. The popular idea is that by applying certain medica ments, healing is achieved, and little or no atten tion is directed to the evil effects produced by dressings of an irritating character. Again, the question of the inimical action of micro-organ isms which gain entrance to a wound is not recognized, hence the carelessness displayed regarding the cleanliness of the patient's sur roundings, the hands of the attendant, and the dressings employed. The primary instruction on this subject, for the amateur, should direct special attention to the fact that cleanliness and efficient drainage are of far greater import ance than the selection of the dressing in the treatment of wounds.

In considering the natural mode of repair it is essential to remember that the reparative activities of the body are directed not only to make good the divided or injured tissues, but to overcome the invasion of micro-organisms. Hence the importance of avoiding in treatment any measures which are likely to interfere with the process of natural repair.

Another point which merits attention is that although it is usual to describe various modes by which repair may take place the general reparative process is similar in all cases, but is subject to modifications, depending on the character and condition of the wound.

In the repair of wounds the usual ultimate result is the production of cicatricial or scar tissue'; this serves as the bond of union and varies in amount according to the degree of approximation of the lips of the wound and the conditions under which healing occurs. It is increased in amount when there is much loss of tissue, when the affected part cannot be kept at rest, and when inflammatory action persists in the wound. Regeneration of injured parts, i.e. restoration of the injured structures to their original condition, only occurs in a few tissues, such as striped muscle, tendon, nerve, and bone. It can only take place when the divided parts are accurately approximated and perfect asepsis is maintained. Regeneration is rarely observed in the case of skin or subcutaneous tissue.

It is now necessary briefly to consider the various stages in connection with the general process of repair, and to draw attention to the modifications induced by the character and con dition of the wound.

The first phenomenon is the occurrence of a varying degree of haemorrhage, which in the case of an incised wound is small in amount. The bleeding is arrested by clotting of the blood in the small vessels. The clots (technically known as thrombi) extend from the mouths of the divided vessels to the nearest patent branches.

In this first stage of the process of repair a number of leucocytes (white blood corpuscles) exude or pass through the walls of the smaller vessels. These leucocytes remove any dead or damaged tissue that is present, and break up and absorb blood-clots. A certain amount of plasma (the fluid portion of the blood) accom panies the exudation of leucocytes so that the process resembles the early manifestation of slight inflammatory action, and provided it remains within certain limits it is regarded as favourable to repair. This is followed by the appearance of large oval cells termed"fibro blasts,"derived chiefly from the cells forming the tissue of the part, the connective tissue, and from the endothelial cells lining the capil laries in the vicinity, the lymphatic vessels and lymph spaces. The result is that a layer of cellular tissue composed of fibroblasts is soon formed and lies on the surface or between the lips of the wound, while the leucocytes disappear.

In the second stage"vascularization"of this layer of fibroblasts takes place. In simple lan guage this implies that the layer becomes sup plied with blood-vessels, i.e. becomes vascular. The process is accomplished as follows: Out growths composed of solid rods of protoplasm spring from the walls of the nearest capillaries. These rapidly increase in length and join with similar outgrowths from other capillaries, or with the wall of another vessel, while connective tissue cells may become spindle-shaped and also join the off-shoots mentioned. Next, the out growths become canalized (i.e. hollowed into fine canals) and communication is established between them and the capillaries, so that blood flows through them, and new vessels are thus formed. The result of the above process is the formation of what is termed granulation tissue. This is composed of loops of capillaries supported by large cells with a varying amount of sub stance between the cells.

The next stage is the transformation of granu lation tissue into fibro - cicatricial tissue. The fibroblasts assume a spindle shape, and subse quently become long and narrow with pointed extremities which often branch. Around them a fibrillated structure is developed, and ulti mately this is changed into the"fibrous tissue of the scar."Contraction of this tissue next occurs and the newly-formed vessels become constricted, resulting in diminished vascularity of the scar tissue, which shrinks, becoming harder in consistence and smaller in extent.

The final stage is reached when the surface of the wound is covered by cuticle, which spreads inwards from the normal epithelium in the vicinity of the wound, especially from the deeper layers of the skin.

Modifications in the General Process of Repair. - As already remarked the general process of repair is modified according to the character and condition of the wound. These modifications may be considered under the following headings: (1) Healing by first intention or primary union; (2) healing by granulation; (3) healing under a scab.

Healing by First Intention. - This takes place in simple incised (clean cut) wounds, when the following conditions exist. (a) A practical freedom from infection; (h) absence of bruising or injury to the lips of the wound; (c) arrest of bleeding, and approximation of the lips of the wound so that it is not possible for an extensive collection of blood or secretions to form between them. Such conditions permit healing to take place in a typical manner as described, the process being complete in a period of from five to seven days.

In veterinary practice, healing by first inten tion is the exception rather than the rule, except in the case of small operation wounds, when the technique is conducted under special conditions so as to ensure freedom from infection (see p. 564). Owing to difficulties which will be con sidered under"Wound Infection"healing by primary union is uncommon in equine practice. In canine surgery, however, this mode of healing is practicable under modern conditions of tech nique and surroundings.

Healing by Granulation. - This is also known as"union by second intention."It is the common mode by which healing takes place in veterinary practice. Formerly, it was believed that suppuration inevitably accompanied the process, but it is now known that if aseptic conditions can be secured, healing by granulation takes place without the occurrence of suppura tion. But in veterinary practice, for reasons which will be indicated later, it is rare to find this mode of healing unaccompanied by the formation of pus.

Healing by granulation occurs under the following conditions: (a) When the lips of the wound cannot be brought into apposition owing to a definite loss of substance, or when no attempt is made to bring about approximation by the employment of sutures. (b) When the surface of the wound is bruised or injured, so that sloughing of a portion of the tissue occurs.

(c) In cases where healing by first intention is prevented by micro-organisms gaining entrance to the wound.

In cases where simple loss of substance occurs, unaccompanied by bruising or infection of the tissues, the blood-flow in the superficial capil laries becomes arrested and the adjacent vessels become dilated. From these latter vessels an exudation of plasma with escape of leucocytes takes place. The plasma coagulates on the

surface of the wound and forms a layer of fibrin, in the meshes of which a number of leucocytes are entangled. This layer gradually increases in thickness, and becomes transformed into granulation tissue in a period of from four to seven days, and subsequently it is converted into fibro-cicatricial tissue and the surface becomes covered by cuticle.

Healing under a Scab. - This process is ob served in small wounds and abrasions, and is practically identical with healing by granula tion, except that repair takes place beneath a scab formed by the drying of the exudation from the wound. When cicatrization is complete the scab is cast off spontaneously. This mode of healing is common in veterinary practice in the treatment of small wounds by the open method, i.e. without any artificial dressing. Not infre quently, owing to infection, pus accumulates under the scab, retarding healing, unless a means of exit is provided.

Wound Infection. - Owing to the fact that infection influences the gravity, course and results of wounds further attention to it is desirable. At one time the occurrence of sup puration in both accidental and surgical wounds was regarded as favourable and healing by first intention was rarely observed. Until Lister in vestigated the subject, and applied antiseptic principles to the treatment of wounds, practi tioners did not realize the importance of surgical cleanliness or the baneful effects of micro organisms on the process of repair. To-day the necessity and advantage of adopting stringent measures to prevent the access of micro organisms to operation wounds is universally acknowledged, while the importance of ener getic treatment of infected wounds is fully recognized.

In human surgery the technique of aseptic (germ-free) methods has reached a high stand ard of perfection, with the result that healing of wounds by primary union is the rule in the large majority of instances.

In veterinary surgery, owing to various circumstances, the difficulties in the way of preventing infection of operation wounds are enormous, so that aseptic methods except under very special circumstances are hardly practi cable. Similar difficulties exist as regards the treatment of accidental wounds.

In considering these difficulties the following points may be mentioned: (1) The Surroundings of Animals. - So far as the horse is concerned it is obvious that even in the best-constructed stable it is impossible to obtain or to maintain conditions for the pre vention of wound infection such as exist in hospitals for human beings. In ordinary stables and surroundings the prevention of infection is far more difficult to carry out.

(2) Ensuring Rest. - Rest is a very important element in bringing about healing by first intention. The difficulties in rendering a part immobile, especially of an equine patient, are well known, the inconvenience and pain caused by a wound not infrequently induce movements of the limbs, while the act of lying down or rising exerts a detrimental effect on the healing process.

(3) Disinfection of the Skin. - This cannot be carried out with anything like the same facility in the horse as in man, even though the part be shaved and painted with tincture of iodine. No doubt these precautions have the effect of lessening the risks of infection, but the ideal aseptic condition of the skin obtained in human surgery is not often attainable in veterinary practice.

(4) Subsequent Treatment. - Unless aseptic treatment can be maintained during the entire care of a wound case the early attempts at ensuring freedom from infection cannot be expected to produce desired results. Hence it would be necessary for the veterinary surgeon to dress the wound with his own hands, as he could not rely on the attendants to observe aseptic precautions. Needless to remark, this course would not be practicable unless the patient were treated in an infirmary. Even with a trained attendant there are many diffi culties in securing ordinary surgical cleanliness.

While admitting the drawbacks as regards prevention of infection in the treatment of wounds in veterinary patients, we must point out the necessity of adopting every means in our power to limit the entrance and develop ment of micro-organisms. As we shall show later, infection varies with reference to the gravity of the results produced, this depending on the virulence of the infecting agent and also on the powers of resistance possessed by the animal. By adopting surgical cleanliness and care in the employment of antiseptics we are often able to prevent the entrance of virulent micro-organisms into wounds, and even if they have been accidentally introduced their develop ment and effects may be overcome by judicious treatment. Hence, there is no excuse for the prevailing notion that because aseptic methods are not practicable to the same extent as in human surgery, it is unnecessary to be particular as regards surgical cleanliness and the adoption of measures to prevent infection of wounds in animals. The fact that a wound is already infected should not render us less careful in pre venting further infection, remembering always that, owing to the surroundings of animals, neglect in this direction may result in the entrance of a more virulent type of micro organism than that already present.

In further consideration of wound infection it is desirable to direct attention to the effects produced by the action of pus-producing micro organisms. According to modem authorities these effects are as follows: healthy reparative action ceases, and is replaced by an inflammatory process of a suppurative type. inflamma tion may be regarded to a certain extent as protective, it antagonizes the action of the micro-organisms.

The suppurative process may be confined to i the wound, or infection may extend adjacent tissues and produce"cellulitis."In deep seated wounds an abscess may be produced.

Various sequel.% may occur from wounds as the result of infection, such as septicaemia (blood-poisoning), erysipelas, malignant cedema, tetanus, etc., these depending on the nature of the infecting agent.

As already pointed out, the term"septic"is one which is not infrequently applied to designate a variety of conditions. From one aspect it is employed to describe a wound which suppurates, in contradistinction to one which is free from germs, i.e. aseptic. In practice, however, the term septic is often reserved for wounds which are offensive or putrid, associated or not with the presence of pus. A large pro portion of wounds in animals heal by granula tion, suppuration to a varying extent is present, but the pus is not offensive, and with ordinary care no complications arise. Such cases are not usually designated as septic, but obviously they cannot be described as aseptic. In order fully to comprehend the principles of the treatment of wounds, it is necessary to know something of the micro-organisms which are responsible for infection and the means at our command to prevent and to combat their action.

The Micro

- organisms responsible for Wound Infection.- The most common, and hence the most important of these in everyday prac tice are included in the group known as the Pyogenic cocci. The following merit special attention: Staphylococcus pyogenes aureus is responsible for the majority of suppurative inflammations, and is often associated with other pyogenic organisms in connection with wound infection (mixed infection). It is very widely distri buted, and is found abundantly in the super ficial layers of the skin. Its power of producing suppuration has been demonstrated experi mentally.

Streptococcus pyogenea plays a very important role in the wound infection of animals. Varieties of this micro-organism probably occur, but owing to a resemblance in their characters it has not been possible to isolate them. The Strepto coccus pyogenea is responsible for spreading cellular inflammation, septic peritonitis occurring as the result of wounds involving the peritoneal cavity, and as a sequel to castration. It has a special tendency to invade the lymphatics and also to induce sloughing of the tissues, and not infrequently it is the causal agent in septicaemia and pyaemia.

Erysipelas,

a form of wound infection, is said to depend on the Streptococcus erysipelatis, but in appearance and cultural characters it re sembles Streptococcus pyogenes so closely that many authorities regard them as identical.

A variety of Streptococcus pyogenes termed Streptococcus equi is regarded by some writers as the causal factor in strangles, but its specific character has yet to be demonstrated. At any rate, we are fully aware of the necessity of guarding against the danger of pus from a case of strangles gaining entrance to wounds.

Amongst other causal agents in wound infec tion we may mention the tetanus bacillus, the bacillus of necrosis, the bacillus of malignant oedema, the bacillus pyocyaneus, and the tubercle bacillus. Wounds may also be in fected by the entrance and development of Botryomyces, the cause of some cases of"collar tumours"and scirrhous cords. In rare in stances a wound may be infected by actinomyces, the organism responsible for antinomycosis or"timber tongue"in cattle.

Not infrequently, more than one variety of micro-organism is responsible for infection of a wound, and from the clinical point of view such"mixed infections"are often difficult to combat.

Modes of Infection.

Having indicated the chief causal agents in wound infection, it will now be necessary to consider the manner in which they gain entrance to a wound. Such knowledge is essential in order to adopt pre ventive measures in dealing with both surgical and accidental wounds.

(1) Infection by Air. - It is now held that germs exist in the atmosphere only in the form of dry dust and that air perfectly freed from dust is harmless to wounds. Moreover, when the air is kept still, wound infection rarely takes place through the atmosphere. But when we consider the surroundings of animals, we must admit the probability of infection through the medium of air containing dust. During the process of grooming the horse, of cleaning out the stall, removing the clothing, and arranging the bedding it is easy to understand how dust impregnated with micro-organisms is enabled to gain entrance to a wound. In the case of operation wounds dust is a prolific source of infection. It may be derived from the bed of straw on which the patient has been cast; also from animals with dirty shaggy winter coats, dust is freely disseminated during the struggles consequent on casting and securing them for operation.

(2) Infection from the Surroundings. - Under the usual conditions of practice it is quite appa rent that aseptic surroundings are difficult if not impossible to obtain. Although every pre caution may be attempted in the initial treat ment of a wound, it is obvious that infection to a greater or less extent is likely to occur from the floor of the stall and from the bedding, more especially in ordinary stables. Without doubt insanitary buildings are a fertile source of infec tion, a fact which has been well demonstrated in connection with the after-treatment of cas tration cases. In such instances septic periton itis is not uncommon as a sequel, when colts are confined in filthy stables. On the contrary, it is rarely encountered when the animals are left on pasture immediately after the operation. The baneful influence of a vitiated atmosphere is also recognized as a factor in the production of sepsis, as it lowers the vital resistance of the patient.

Similar remarks apply to the results obtained in the treatment of all types of wounds when the animals are kept in filthy surroundings, as under such conditions the most virulent forms of infection are likely to occur.

(3) Infection from the Operator or the Attend ant. - This constitutes a very serious and im portant source of infection, and one that is not infrequently overlooked. A prevalent idea is that with a free use of antiseptic agents the risks of infection from the hands of the operator or attendant may be ignored. Practical experi ence has shown the necessity for surgical clean liness in connection with the hands and other details relating to the care and dressing of wounds. Judging by the neglect which is not uncommonly displayed in relation to wound dressing, one may be pardoned for expressing surprise that a greater number of serious cases of wound infection do not occur. The natural power of resistance to infection which is so highly developed in many animals explains how carelessness in connection with the dressing of wounds is not always followed by serious if not fatal results.

Infection likely to arise from contaminated hands is preventable by the exercise of simple measures of cleanliness, yet we know how diffi cult it is to get such measures carried out in practice. The energetic use of a nail-brush with soap and water is essential before rinsing the hands in a disinfectant solution. Obviously, it would be courting disaster to perform an operation or to dress a wound immediately after opening a strangles abscess, dressing a wound in a case of septicmia or one of tetanus, or con ducting a post-mortem examination. Under such conditions the veterinary surgeon should postpone operations or the dressing of wounds until such time as he can render his hands surgically clean, and we may add that when the hands have been contaminated a very thorough and prolonged disinfection is necessary to cleanse them.

(4) Infection from Surgical Dressings, etc. - Carelessness in dealing with surgical dressings and utensils employed in the treatment of wounds is responsible for many cases of infec tion. Repeated instruction is required before the ordinary attendant can be made to recognize the importance of keeping surgical dressings such as cotton wool, gauze, etc., free from con tamination. Too often they are placed on the floor during the dressing of the wound, or they may be soiled by the hands of the dresser, and thus act as a carrier of infection. Similar remarks apply to the solutions employed and the vessels containing them. The popular idea is that provided an antiseptic is added to the water the cleanliness of the latter is not of much importance, while little care is given to the condition of the vessel containing the solution. Another fertile source of infection is the employ ment of sponges which have become contain mated by previous use, or as not infrequently happens, have been utilized for various purposes in the stable. Sponges, other than those specially prepared for surgical use, are unsafe and should not be used. Swabs of cotton wool which can be discarded after each dressing are safer and quite as serviceable.

Infection from Sutures. - The necessity for ensuring that sutures are in an aseptic condition cannot be too clearly emphasized. This point will be again referred to under"suturing of wounds." Infection from Instruments. - Every modern practitioner recognizes the necessity for steril izing instruments prior to use, and is aware that by boiling them for fifteen minutes all danger of infection from this source can be removed.

The instrument which in the hands of the layman is a frequent source of infection is the syringe used for injecting wounds. Needless to remark, it is exceptional to find this instrument really clean or disinfected, and the use of a contaminated syringe is more likely to intro duce infection than to destroy germs already existing in a wound. Obviously no syringe except one that is capable of being sterilized by boiling should be employed by either professional or layman.

Circumstances predisposing to Infection in Wounds. - Certain conditions are especially liable to favour infection in wounds. These may be classified as follows: (a) Deficient Drainage. - Unless a means of escape for the discharge of serum is provided, this material accumulates within the wound and forms a suitable nidus for the development of micro-organisms. The amount of this dis charge varies according to circumstances, and is especially profuse in the case of lacerated wounds. A typical example is found in cas tration wounds, in which instance, unless the openings in the scrotum are made of length, the skin wounds heal rapidly, a large amount of serous discharge accumulates, and if this is not liberated it soon becomes putrid, leading to unfortunate results. The retention of blood-clots in a wound is also an important factor in favouring infection, as they form a nidus for micro - organisms. The subject of drainage will be again referred to under the treatment of wounds.

(b) The Presence of Bruised or Necrotic Tissue in a Wound. - When tissues are braised their vitality is either weakened or destroyed and they offer no resistance to the invasion and development of micro-organisms. Hence the necessity for removing all devitalized tissue in the treatment of lacerated wounds. Another point of importance in connection with surgery is that all necessary manipulations should be carefully conducted so as to inflict as little damage to the tissues as possible.

wound, infection, healing, process and animals