After having studied the mode of action of hypochlorites, Dakin was led to investigate the substances which act in a manner almost identical, but which are of greater practical value. He believed that the bactericidal action of hypochlorites took place by means of substances formed at the expense of proteins, and containing chlorine in combination with nitrogen. Experiment showed him that when proteins such as blood-serum, white of eggy casein, etc., are treated by hypochlorites, they give rise to products of a high antiseptic potency. These substances, without a doubt, are formed in situ when wounds are treated by hypochlorites. Thus, after the disappearance of free hypochlorite, there still remains in the wound a substance having antiseptic power.
Certain aromatic chloramines which form soluble salts give encouraging clinical results. The best of these compounds are the benzene- or the para-toluene-sodium-sulphochloramines which have been described by Chatta-way.
These substances, which possess a very high antiseptic potency, are but slightly irritating, and can be used in a much higher degree of concentration than the hypochlorites. The solutions in general use in our experiments vary from 0.2 per cent. to 2.0 per cent. The action of these substances is similar to that of the hypochlorites, but their antiseptic potency is superior.
1. Bactericidal Action. - Staphylococci suspended in water are killed in two hours by benzene-sodium-sul-phochloramine at a strength of 1: 500,000, and by para-toluene-sodium-sulphochloramine at a strength of 1: 1,000,000. When horse-serum is present, the strength necessary becomes 1: 1,500 to 1: 2,500. The B. pyo-cyaneus, Eberth's bacillus, and the bacillus coli are slightly more resistant than staphylococci, whilst B. perfringens and streptococci are more easily killed.
On infected wounds chloramines give results similar to those of hypochlorite of soda. Their action on microbes has been determined in the course of a great number of experiments similar to those we have described when on the subject of hypochlorite of soda. Used with the same technique they sterilise wounds. Their action on the tissues has been studied on both sterile and infected wounds, by comparing the charts of sterilisation and the curves of cicatrisation. When used at a strength of less than 0.2 per cent. they do not interfere with the rapidity of repair. It has been observed sometimes, however, that an aqueous solution of 2 per cent may produce lesions of the connective tissue which show themselves by diminution, and sometimes arrest, of cicatrisation.
With the collaboration of MM. Cohen, Daufresne, and Kenyon, Dakin investigated a certain number of substances of the same group, particularly the chloramines, in which the group NCI is separated from the benzene radicle by the group SO2Na; the similar naphthalene derivatives; the other similar dicyclic derivatives; the chloramines in which the group NCI is directly attached to the benzene radicle; the brom-amines; and finally the products of the action of hypochlorites upon different proteid substances. He found that the substances which contain the group NCI also possess powerful bactericidal action. But the presence in their molecule of more than one NCI group does not increase their germicidal potency. Molecule for molecule, the germicidal action of many of these chloramines was greater than that of hypochlorite of soda. As to the substances derived from proteins under the influence of hypochlorite of soda, their antiseptic action was very powerful. But blood serum inhibited their potency, as it had done in the case of hypochlorite of soda and the aromatic chloramines.
While inquiring into the factors which control the germicidal action of chloramines, Dakin found that chloramines or bromamines destroy micro-organisms at a lower molecular concentration than the corresponding hypochlorites or hypobromites. They may not, therefore, be considered as the bio-chemical equivalents of these latter substances.
The germicidal action of chloramines is due to the fact that the substances such as proteins, amino-acids, urea, and ammoniacal salts, which constitute living organisms, contain nitrogen under a form which can attract the chlorine of the different species of chloramines. On the other hand, the chlorinating action of chloramines resembles that of the hypochlorites, but their antiseptic action is often much greater. This fact may be attributed, according to Dakin, either to a special obscure action of the chloramine molecule, or possibly to the elective chlorination of some constituent of the cells.
2. The Properties of Para-toluene-sodium-sulphochlor-amine. - Because of these many excellent qualities, para-toluene-sodium-sulphochloramine was chosen by Dakin for practical use in the sterilisation of wounds. This substance can readily be manufactured at a reasonable price by a method which has been described by Dakin. Para-toluene-sulphochlorate, a by-product in the manufacture of saccharine, is the basis. Several English houses are making it, and sell it under the name of "Chloramine T." Apart from its great germicidal potency, which has been noticed above, Chloramine T has other advantages. It does not coagulate proteid matters in the ordinary treatment of wounds. It is very soluble in water. That is an important factor. In short, chloramines, endowed with a high germicidal potency, very slightly soluble in water, but which could be dissolved in vaselin or lanolin, would be without practical value. Besides, Chloramine T has the advantage over hypochlorite of being very stable. Dakin found that the decomposition of a solution kept in the dark for 132 days, was inappreciable, whilst the solution exposed to daylight showed such a slight diminution of strength as to be scarcely noticeable. This stability of Chloramine T is a great advantage over Dakin's hypochlorite solution, which decomposes under the influence of light and heat.
Dakin's chloramine is employed in an aqueous 1 per cent. solution. As its stability is greater than that of hypochlorite, it has been employed by Daufresne in the form of a paste, composed of stearate of soda mixed with varying proportions of chloramine. For general purposes a paste is used which contains 1 per cent. of chloramine and S'6 per cent. of stearate of soda.
3. The Interaction of Chloramine and the Tissues. - Chloramine, employed on the surface of a wound, in solutions of about 1 per cent., produces no retardation of cicatrisation. A large number of wounds have been treated with Daufresne's paste of sodium stearate, containing 4 to 10 per cent. of chloramine, and the observed curve of cicatrisation always coincided with the curve calculated by du Nouy's formula. Fig. 28 shows the cicatrisation curves of a wound treated with a 10 per cent. paste of chloramine. Moreover, experiments made by Daufresne showed that a fragment of skin placed in a solution of chloramine retained its normal dimensions after the lapse of several days. The same is true of mortified tissues situated on the surface of wounds. In experiments conducted in vitro as well as in direct observations of wounds, it was found that chloramine does not dissolve the tissues. This is why it does not cleanse the surface of wounds as Dakin's solution does. It is not irritating, but it lacks one of the most necessary properties of an antiseptic, that of dissolving necrosed tissues. It should therefore be reserved for wounds whose surface is already cleansed, or for the skin and the mucous membranes.
While chloramine has little action on the tissues, the tissues, on the other hand, have a very marked action upon chloramine. Experiments were made with the peritoneum of a cat. When a 0.25 per cent. solution of chloramine is placed in a small cup containing a portion of the epiploon provided with its normal circulation, the rapid destruction of the antiseptic substance is observed. As a rule, the strength of a 0.25 per cent. solution of chloramine falls to 0.14 or 0.15 per cent. in about two minutes. Its decomposition is therefore much less rapid than that of hypochlorite. Chloramine will often lose only half its strength, while Dakin's hypochlorite loses more than four-fifths.
These experiments show that chloramine, despite its much greater staoility, is rapidly decomposed when in contact with the tissues, and a considerable volume of solution must be employed to sterilise a wound.
In the sterilisation of a wound, the antiseptic plays a part comparable to that of the scalpel in a surgical operation. It is only an instrument, and does not constitute a method. But the choice of a good instrument is a factor indispensable to success. Chloramines and Dakin's hypochlorite are admirable instruments.
As Dakin's hypochlorite has the advantage of being strongly bactericidal, and only slightly irritating to the tissues, and at the same time can be readily manufactured at a cheap rate, it would seem that it ought to become the chosen antiseptic during this war.