The antiseptic properties of hypochlorite of soda have been known for a very long time.1 But it is not possible to use hypochlorite, either in the form of eau de Javel or of Labar-raque's solution, for the sterilisation of wounds, because these solutions are irritating, and may cause grave injury to the tissues. Because of this, Dakin endeavoured to lessen the irritant qualities of the hypochlorites without modifying their antiseptic action.

1 Dakin, British Medical J'ournalt 1915, p. 809.

The principles of the preparation of the hypochlorite solution by Dakin are as follows. A solution of hypochlorite of soda almost always contains free alkali, even when it is prepared with the greatest care. Though looked upon as neutral, it has an alkaline reaction. This reaction is due not only to the alkali which may arise from the mode of preparation, but also to a hydro-lytic dissociation of the hypochlorite which produces free soda and hypochlorous acid.

The amount of this dissociation has been measured by Duyk, and is quite considerable. It is to the formation of free alkali, therefore, that the irritating action of hypochlorite is due. The amount of the hydrolytic dissociation increases with the dilution, so that, from a practical point of view, a hypochlorite cannot be rendered non-irritant by merely reducing its concentration. Really, a point is soon reached at which the bactericidal action is lessened, while the irritating properties of the solution remain. Besides these two sources of free alkali, it must not be forgotten that soda may be liberated by the action of hypochlorite on proteins. A reaction takes place, in which the chlorine of the hypochlorite attaches itself to the nitrogen of the proteins, as will be demonstrated later.

Dakin, for the neutralisation of the alkali of the hypochlorite of soda, made use of the following known facts. Blood and other organic liquids, and also certain artificial saline solutions containing mixtures of polybasic acids, such as phosphoric acid, are able to keep their essential neutrality, even after the addition of acid or alkali. This phenomenon is due to the fact that the addition of acid or alkali simply changes the relative proportion of two or more salts of the polybasic acid present in the solution. Setting out from this principle, and employing a feeble polybasic acid (boric acid), Dakin succeeded in preparing a simple mixture of hypochlorites, which remains very nearly neutral under all conditions, and which in consequence does not irritate the tissues. This solution contains a mixture of hypochlorite and polyborate of soda and small quantities of free hypochlorous acid and boric acid. In this manner the irritating action of caustic soda is avoided. In fact, if alkali should form, it would be immediately neutralised by the boric acid and the acid borates present in the solution.

Dakin's hypochlorite differs from eau de Javel and Labarraque's solution in that its destructive action upon the tissues is very slight. Study of the communications made to the learned Societies of Paris, and particularly to the Academie de Medecine, shows that the necessity for using a non-caustic antiseptic has not been grasped. Surgeons do not yet comprehend that Dakin's solution, containing no free alkali, can be employed under conditions where the use of eau de Javel or Labarraque's solution would be absolutely impossible.

A simple experiment made by Daufresne in the laboratories at Compiegne will show the essential difference which exists between Dakin's solution, on the one hand, and eau de Javel and Labarraque's solution on the other. In three tubes there were placed Dakin's solution, eau de Javel, and Labarraque's liquor. The strength of the three solutions in hypochlorite of soda had previously been brought to 0.5 per cent. A fragment of skin from a still-born infant was placed in each of the three tubes. At the end of two hours the action on the skin of eau de Javel and Labarraque's solution was already manifest. The skin was greatly swollen, and the slightest friction could detach the epidermis in a fragile pellicle. In the hours following the process continued, the fragment became completely transparent, and after twelve hours in eau de Javel, and fourteen hours in Labarraque's solution, the fragment of skin was completely dissociated. The tubes contained only a powdery sediment. The piece of skin placed in Dakin's solution behaved in quite a different manner. After two hours of contact the epidermis was still very adherent, and the aspect of the skin was normal. At the end of twenty-four hours the alteration in the tissues resembled that observed after two hours' contact with the solutions of Javel and Labarraque.

This experiment shows in a very clear manner the profound difference which exists, from the biological point of view, between Dakin's solution and the non-neutralised hypochlorites. In a word, Dakin's researches allow us to use to-day hypochlorite of soda under conditions such that it will sterilise the tissues without danger to them. We shall see, later, that the hypochlorite only kills the microbes when its action is extended over a long period, and it is of a strength of 0'5 per cent. (about), conditions impossible to realise if the solution be caustic.

It is possible to obtain a solution even less irritating than Dakin's solution, if we prepare it by the electrolytic method. Electrolytic hypochlorite has not hitherto been employed in surgery on account of its defective keeping properties. As it is completely devoid of alkali, its concentration diminishes very rapidly, and in a few hours its bactericidal power may become insufficient. In the course of experiments carried out in the Com-piegne laboratories, Dakin discovered that electrolytic hypochlorite, that is, hypochlorite completely free from alkali, may be rendered stable by a small quantity of permanganate of potash or silicate of soda. Hypochlorite thus prepared will keep for several weeks without any appreciable loss of concentration. It is less caustic than the chemically prepared solution. Its power of dissolving necrosed tissues was compared with that of Dakin's solution by placing, in the two solutions, fragments of skin of identical dimensions (Fig. 1). The skin was destroyed more rapidly in Dakin's solution than in the electrolytic solution. Nevertheless, the solvent power of the electrolytic hypochlorite was sufficient to rid wounds of the necrosed tissues which occurred upon their surfaces.