The object of the bacteriological examination is to demonstrate the progress of sterilisation and to mark the moment at which this sterilisation is advanced sufficiently to allow of effectual closing of the wound. It is necessary that the quantity of microbes contained in the wound should be known. Since wounds should be examined every two or three days, and as in most hospitals there is no bacteriological specialist, the technique has been made so simple that a large number of examinations can be made by those possessing little experience in bacteriology. The secretions of the wounds are studied by means of "smears." This summary proceeding allows certain qualitative reports to be made, but, more important, it allows of an approximate enumeration of the microbes contained in the secretions. Thanks to it, the diminution in the numbers of the microbes can be made known as the treatment progresses, up to the date of their total disappearance. We have determined empirically that the disappearance of microbes from the smears indicates a degree of asepsis compatible with closure of the wound. In spite of its crudeness, this method is to be preferred to the usual procedure of bacteriology. In truth, "smears" show what the wound contains, while cultures indicate what may grow under certain conditions. Cultures must be relied upon if it is desired to learn if a wound is bacteriologically sterile, or when it is important to know not only the volume but the nature of the infection. The culture method may also be used in that stage of infection in which smears do not give reliable information, that is to say, during the first twelve hours. At this period, in fact, microbes are in such small numbers, and so diluted by the blood, that they cannot be seen in the smears.

A. Technique, 1st. Method Of Taking Specimens Of The Secretions

During the first six or twelve hours secretions are absent from the wound. The walls bleed more or less freely, and smears of blood taken from the wound show no microbes. Specimens should be taken from the parts of the wound which are not bleeding, in the neighbourhood of, or from the surface of, shreds of clothing or shell splinters.

Wounds older than twelve hours usually have some secretion. As the haemorrhage is arrested, secretions can be taken easily from a region where the secretions are not diluted by blood. Always the points chosen are in contact with shreds of clothing or bits of shell, for in these regions the primary infection is to be found at its maximum.

The specimen is taken by means of a rigid platinum wire mounted on the end of a glass rod (Fig. 66). Should the wound be undergoing continuous instillation, the treatment must be interrupted for two hours at least, before the time when the specimen is to be taken, in order that the secretions may not be diluted by hypochlorite. The tubes are withdrawn and the compresses removed with the greatest gentleness, in order not to provoke haemorrhage. The spot from which the specimen is to be taken is chosen with minute care. It must never be taken from a region of the wound which is bleeding. That region is sought for where there is the greatest probability of finding microbes. As the smooth surface of muscle is very quickly disinfected, for preference one examines the greyish structures which are found in the deepest parts of wounds, necrosed points of fascia, the surface of damaged bone or the culs-de-sac of irregular wounds, where secretions can accumulate protected from the antiseptic liquid. It is by means of multiple specimens taken from various parts that one can ascertain the bacteriological condition of a wound. In surface wounds, it is useful to examine the neighbouring skin. With the aid of a bistoury or a rigid platinum wire the surface of the skin or the epithelial border is lightly scraped.

Fig. 66.   Taking a specimen.

Fig. 66. - Taking a specimen.

2nd. Preparation of the Slides. - The secretions thus collected are spread out on microscope slides (Fig. 67) which are furnished with a label upon which are written the name of the patient, his number, the character of the wound, and the region of the wound whence the secretion was taken. The slides, thus prepared during the course of a round of visits, are arranged in a box for microscope specimens, where they dry, and are taken to the laboratory, where a nurse fixes and stains them.

Each slide is held between the thumb and index-finger, and passed three times through the flame of a Bunsen burner, the smear being turned towards the flame.

Fig. 67.   Making a smear.

Fig. 67. - Making a "smear."

Then it is placed on a glass support and receives a few drops of carbolised thionin. After half a minute, it is washed with water and put aside to dry.

3rd. Counting the Microbes. - The slides thus stained are arranged upon a table, and the nurse places on each smear a drop of oil of cedar. The preparations are then examined with a No. 12 immersion objective and a No. 3 eyepiece. The number of microbes found in the field of the microscope are counted, and the anatomical elements which are found there are also scrutinised. This technique gives naturally only crude results, but they are adequate. In fact, when the number of microbes per microscope field exceeds fifty or a hundred, it is useless to count them more precisely. The examination of the smears has but one object, to indicate the progress of treatment. Hence it is easy to note that a secretion, one day containing innumerable microbes, shows the next day a marked diminution in their number. Should the number drop below fifty per microscope field, counting is easier. When it is a question of closing a wound, half a score fields should be looked over carefully. When the smears no longer yield microbes, or only one to five or six fields, then the surgeon should be notified as to the possibility of suture.