The method we have just described permits a large number of wounds to be examined in a short time. But it is far from being exact. So we must inquire if the simple counting of microbes on a smear gives sufficient information of the bacteriological condition of the wound.
The technique carries with it obvious possible sources of error. In the first place, the smears are of varying thickness, according to the nature of the secretions and the manner in which they are spread out on the surface of the slide. Next, the counting of microbes contained in a microscope field is of necessity far from being exact. If it were a question of finding out precisely the quantity of microbes contained in any given volume of secretion, the method would be absolutely inadequate. But we are not here engaged in scientific research. We desire nothing more than a clinical indication. In a word, the surgeon seeks to learn if the quantity of microbes in a wound under treatment is lessening, and when these disappear completely.
To appreciate the diminution in the number of microbes contained in the secretions of a wound, it is of little moment that mistakes of considerable magnitude may be made in the counting. Errors of ten per cent. or even thirty per cent. are of no great importance. If one day there is found in the pus an uninterrupted mass of microbes, and the next day only a hundred per microscope field can be counted, it is evident that their number has lessened. It really matters little that there may have been two hundred or even fifty, instead of a hundred (Figs. 85 and 86). And in the same way, if on the following day one counts ten, per microscope field, it is of minor importance that an error of twenty-five per cent. or of fifty per cent. may have been made, because it is certain that the volume of infection has diminished. To sum up, important mistakes in counting do not prevent us from marking on the bacteriological charts the progressive lessening of infection, because the variations in the quantity of microbes under the influence of treatment are very considerable (Figs. 85 and 86-88). Besides, experience has shown that if the examinations are made by the same person under identical conditions, the results are quite consistent, and that the evolution of the wound under treatment can be followed with quite sufficient accuracy.
The date of the disappearance of microbes is indicated with ample precision by the preceding methods. From the time when the secretions contain only half a score microbes per microscope field, counting becomes easier (Figs. 85 and 87). It can be done with still more precision when only one or two microbes per field are to be found (Fig. 88). If the secretions collected from the different regions of a wound do not contain more than one microbe to five or six fields, the wound may be looked upon as being surgically sterile.
Fig. 85. - Curve representing the sterilisation of the wound in case 318. Jan. 10, the wound contained a large number of microbes. On Jan. 16 only one per microscope field could be found, and by Jan. 20 microbes had completely disappeared from the smears.
At the same time, clinical signs must not be altogether lost sight of. In reality, a wound whose secretions no longer yield microbes in the smears, may still be infected. When a wound has suppurated during a long period before being submitted to chemical sterilisation, microbes are already encapsuled in the scar-tissue (englobe, Fr.). The surface of the wound may be sterile, while microbes remain latent in the deeper parts. In this case, the clinical history indicates to the surgeon that the deeper portions of a wound, sterile in appearance, may be infected; and that in closing such a wound it is not prudent to make use of deep interstitial sutures, which of necessity would set up reinfection. In wounds which have never suppurated, and of which the secretions are sterile, diverticula may have succeeded in escaping the antiseptic liquid, and may serve as a refuge for microbes. That is the reason why the temperature should always be taken. If a man whose wound is to all appearance sterile has an evening temperature of 37.8° or 37.9° C.(100° or 100.20 Fahr.), it is probable that a little pocket is cut off from the main cavity and is not completely disinfected.
The disappearance of microbes from the smears by no means implies that the wound is really aseptic. It simply indicates that the degree of sterility compatible with closure of the wound has been attained. We are seeking, in fact, surgical asepsis, not bacteriological asepsis.1 In the majority of cases, the secretions of wounds whose smears no longer yield a microbe still give positive cultures. Certain writers - for example, Policard 2 - even believe that chemical sterilisation never achieves absolute asepsis of a wound.
Very large wound of the posterior region of the leg (Case 318). Fig. 86. - Jan. 10. More than 100 microbes per microscope field. Fig. 87. - Jan. 12. About 10 microbes per field. Fig. 88. - Scarcely one per field. (The illustrations represent only the central part of the field of the microscope.)
[Toface page 202.
Another bacteriologist, M. Tissier,3 considered that the absolute asepsis of war-wounds was impossible of achievement, even after protracted treatment. This conclusion merely shows that the technique employed in the cases under M. Tissier's observation was insufficient. By means of suitable technical methods, indeed, the surface of a wound can be rendered so aseptic that cultures from its secretions remain sterile. M. Vincent,4 in the Compiegne laboratories, carefully examined a certain number of wounds. He found that in six out of nineteen injuries treated by the usual technical methods by MM. Guillot and Woimant, bacteriological asepsis had been obtained. In short, 30 per cent. of the wounds treated without special attention in the wards of the Compiegne hospital were aseptic. The proportion of bacteriologically aseptic wounds might have been increased by a more meticulous treatment. Whatever the nature of the infection, the wounds became sterile. Those infected by streptococci were sterilised less rapidly than the rest, but they too became aseptic. We do not seek to obtain bacteriological asepsis,5 for this is unnecessary, experience having shown that surgical asepsis, revealed by the disappearance of microbes from the smears, is sufficient in practice.
1 Pozzi, Bulletin de l Acade'mie de Medecine, meeting Jan. II, 1916.
2 Policard, loc. cit.
3 Debeyre and Tissier, C. R. Sociite de Chirurgie, March 20, 1917.
4 Vincent, Journal of Experimental Medicine, 1917.
5 Pozzi, Bulletin de l Academic de Medecine, Jan. 11, 1916.
However, by the aid of a precise technique, the surface of a wound can be rendered so aseptic that cultures from its secretions remain sterile. But this degree of asepsis is of no practical interest.
Finally, bacteriological examination in the simplified form we have just described, should be looked upon as an indispensable part of the method of wound sterilisation, because it allows the progress of treatment to be followed step by step, and indicates that it should be modified if the number of microbes does not steadily lessen. Alone, it can point out the moment when a wound may be closed. Indeed, a wound should never be sutured if one is ignorant of what it contains. Despite its lack of scientific precision, the study of smears gives to the surgeon clinical information which is indispensable for the direction of treatment.