In order to choose the fittest substance to sterilise an infected wound we must consider, apart from its bactericidal action, many other factors, such as its capacity for irritating the tissues, its toxicity, its solubility, its power of penetrating the tissues, and of being absorbed by them, and the manner in which it reacts with proteids and other constituents of the tissues. The destruction of bacteria under the influence of a chemical agent is due to the reaction of the antiseptic on the one side, with, on the other, proteins and other substances which enter into the constitution of micro-organisms. Suspended in water, microbes are easily destroyed by antiseptics, because the mixture contains no other proteins. But when they are immersed in blood serum, pus, or other exudations, their destruction is more difficult, because the antiseptic acts not only on the micro-organisms but also on the protein substances in the midst of which they are found. That is precisely why the value of a substance intended for the treatment of wounds, should be judged according to its bactericidal action on microbes in suspension in blood-serum and pus, and not upon microbes simply suspended in water.

The bactericidal activity of all known antiseptics is greatly reduced by the presence of blood-serum or analogous substances. This reduction is so great in certain cases that the substance employed under these conditions practically loses all its value. Dakin and Daufresne have shown, in the experiments described later on, the enormous diminution in bactericidal power of certain antiseptics under the action of blood-serum. In these experiments the antiseptic action of substances was estimated by the degree of concentration of the solution capable of destroying in two hours, at the temperature of the laboratory, microbes in suspension in water and in horse-serum.

The technique followed by Daufresne was as follows: A series of tubes was prepared containing 5 cubic centimetres of a solution of the substance of a degree of concentration progressively diminishing. To each tube was added one or two drops of a culture (twenty-four hours in peptonised bouillon) of the organism to be studied. A control-tube was at the same time prepared containing 5 c.c. of distilled water with one drop of the culture. The mixtures of antiseptic and microbes were carefully shaken every half-hour, and kept at a temperature of 18° to 200 C. for two hours. Afterwards a loopful of the liquid from each tube was placed in each of a series of tubes, each containing 3 c.c. of bouillon. These tubes were placed in the incubator for twenty-four hours, and kept at a temperature of 370 C. When, at the end of twenty-four hours, there was no development, it was decided that the degree of concentration of the antiseptic was sufficient to kill the organism. Incomplete sterilisation was indicated by the growth of the organism in the bouillon. Examination of the antiseptic action of the substance in presence of blood-serum was made in a similar manner, but to the liquid contained in the first series of tubes were added 5 c.c. of horse-serum, previously warmed to a temperature of 550 or 560 C.

In this fashion some two hundred substances were studied by Dakin and Daufresne. The micro-organisms which were used as tests were staphylococci, streptococci, the bacillus pyocyaneus, and the bacillus of Welch. In the following table will be found the results of some of Daufresne's experiments, made by means of a fresh culture of staphylococci on certain antiseptics in daily use. The sign 4- indicates that the culture is positive, and the sign - that it remained sterile.

Antiseptics.

Without blood-serum.

With blood-serum.

Acid carbolic ..........................

1

:

250 -

1

:

50 -

" "

1

:

500 +

1

:

100 +

Acid salicylic .........................

1

:

2,500 -

1

:

100 -

" "

1

:

5,000 +

1

:

250 +

Hydrogen peroxide ....

1

:

3,500 -

1

:

I,7O0 -

" " ....

1

:

8,000 +

1

:

2,000 +

Iodine ................................

1

:

100,000 -

1

:

I,000 -

" " ........................

1

:

10,000,000 +

1

:

2,500 +

Bichloride of mercury . . .

1

:

5,000,000 -

1

:

25,000 -

" " ...

1

:

10,000,000 +

1

:

50,000 +

Nitrate of silver ..................................

1

;

1,000,000 -

1

:

10,000 -

" " .............................

1

:

10,000,000 +

1

:

25,000 +

Hypochlorite of soda ....

1

:

500,000 -

1

:

I,500 -

" " ••••

1

:

1,000,000 +

1

:

2,000 +

This table shows wha1t feeble power is pos1essed by an antiseptic which has had a great vogue - carbolic acid. It also demonstrates that bichloride of mercury, which has only a mediocre action on an infected wound, nevertheless kills the staphylococcus in presence of blood-serum of 1: 25,000. These experiments clearly show us that in the choice of a suitable antiseptic many qualities beside bactericidal action have to be considered; it has been demonstrated that bichloride of mercury, nitrate of silver, and iodine, which have a high germicidal potency, are nevertheless the least suitable for wound treatment. Therefore it is well to become acquainted with the practical inconveniences of the substances we are about to examine.

Phenol has a very poor bactericidal power, especially when acting in the presence of blood-serum. If employed in concentration sufficient to render efficient its germicidal action, it becomes highly destructive to normal tissues.

Hydrogen peroxide solution gives encouraging results whose bactericidal action is examined in a test-tube, But the wounds, on the contrary, it has a very feeble action, because it decomposes with the greatest readiness under the influence of the catalysis always going on in the tissues and in the blood corpuscles. Consequently, its action is only exerted during a comparatively insignificant period of time. The mechanical detergent action which results from the rapid disengagement of oxygen when in contact with infected surfaces, has probably a greater value than the antiseptic action of the hydrogen peroxide itself. Dakin1 quotes on this subject an interesting experiment which had been communicated to him by Prof. E. K. Dunham of New York. A rabbit which had received an intra-venous injection of Welch's bacillus (Bacillus aerogenes capsulatus or Bacillus perfringens) was killed. The infected liver was cut up very carefully into tiny fragments. Placed in the incubator with hydrogen peroxide solution, it was found that the volume of a fragment of infected liver must not exceed a millimetre cube, if the micro-organisms contained in it were to be killed. Should the fragments be a little larger, the bacilli of Welch multiplied actively. Hydrogen peroxide, therefore, may be considered as having but a feeble antiseptic action, even against anaerobic microbes.