This is why we must employ a substance capable of destroying all the anatomical elements deprived of circulation. The concentration of Dakin's solution is such that it enables us to utilise the different degrees of resistance presented, on the one hand, by the microbes, the free anatomical elements, and the necrosed tissues; and, on the other hand, by the normal tissues provided with circulation. It destroys the former and respects the latter.

1 Rous and Jones, Journal of Experimental Medicine, 1916, p. 601.

(c) Action of Hypochlorite on Tissues equipped with a Circulation. - In order to appreciate the action of Dakin's solution on living tissues we have investigated the progress of cicatrisation of wounds treated with hypochlorite.

Certain technical difficulties are presented by this research. It is essentially necessary that the conditions of the wounds whose healing is being studied, and particularly their microbial state, should not vary throughout the duration of the experiments. Should these conditions vary, one may no longer attribute to the substance employed the eventual modifications in the progress of cicatrisation. Furthermore, the surface of wounds, in spite of the irregularity of their outline, must be measured exactly.

Up to the present, no one has taken the trouble to study in any precise manner the factors capable of modifying the rapidity of cicatrisation. The bacteriological condition of wounds the subject of experiment has not hitherto been taken into account. It is recognised, however, that the presence of microbes on the surface of a wound has a profound effect on the progress of repair. In all the forms of technique hitherto employed, this truly important omission destroys the value of all the experiments on and observations of substances supposed to aid cicatrisation. This error in technique explains the contradictions found in all medical publications on the subject of topical applications in the treatment of wounds. Every surgeon attributes a power more or less marvellous to some substance which the surgeon of the next hospital looks on as insignificant.

In the same way, estimation of the progress of cicatrisation has always been left to individual opinion. As a matter of fact, it has never been sought to devise a technique which would permit exact measurement of the surface of a wound, with estimation in square centimetres of the amount by which it lessens day by day. The ignorance we manifest, after so many ages of surgical practice, of the real influence of the substances used in treating wounds, is only due to the absence of scientific method. To obtain exact data on this subject, it was necessary in the first place to experiment on wounds placed under conditions which remain unchanged throughout the duration of the observations, and afterwards to devise a method which would allow the progress of cicatrisation to be measured.

(a) The Conditions of the Wounds. - The wound must be that of a man immobilised in bed, and whose general state does not vary during the period of observation. The bacteriological state of the wound plays an important part in the progress of cicatrisation. Rapidity of repair varies according to the nature and the volume of the infection. When microbes are allowed to multiply on the surface of the wound, it is impossible to know if the modifications of cicatrisation are due to direct action of the substance experimented with upon the tissues, or to a favourable or unfavourable action of this substance on the microbial flora; or to the algebraic sum of the two causes. Therefore the daily control of the state of the wound, by means of the microscope, is indispensable, to avoid a false interpretation of the experimental results.

The experiments were made on surface wounds, and sometimes on deep wounds. Wounds of regular perimeter were preferred to those whose margins were torn. Wounds of elongated form were specially chosen, so that one half could be treated by a substance, while the other half served as a control. Or, better still, wounds of nearly equal size were used, situated in the corresponding region in the same individual One of the wounds was dressed with a substance to be tested, while the other served as a control.

Every day the bacteriological condition of the wound was examined by the aid of "smears," and sometimes of cultures. As microbes were found, steps were taken to eliminate them. The granulating surface and the neighbouring skin were washed carefully with neutral oleate of soda. Then the granulations were sterilised by means of hypochlorite of soda or chloramine. When the bacteriological examination showed that sterilisation was complete, the wound was dressed, either with oleate of soda, or with stearate of soda containing small quantities of antiseptic, or with vaselin, or saline solution. In this manner it was possible to keep wounds almost completely aseptic. The daily bacteriological examination allowed reappearance of the infection to be discovered, and allowance to be made for it in the interpretation of the experiments. On wounds thus prepared the action of the substances was studied.

{b) Technique of the Measurement of Wounds. - In most cases the progress of repair was studied on surface wounds, and only rarely in deep wounds. The surface of a wound was measured in the following manner. A sheet of thin celluloid was applied over the surface of the wound. By the aid of a pencil (used for marking glass) the outline of the epithelial margin was traced, and in every case where it was possible, the contour of the cicatrix at its union with sound skin. The drawing thus obtained was transferred to a sheet of ordinary paper. Then, with the aid of a planimeter, the area of the wound, properly so called, was measured, also that of the surface of the wound increased by that of the cicatrix. Thus in square centimetres was obtained the area of the two surfaces, and, by subtracting the first from the second, the area of the surface of cicatricial tissue was obtained. When a deep wound was in question, its capacity was obtained by filling it with water and so measuring the volume.