ANTISEPTICS and ASEPSIS. Antiseptics are substances used for the prevention of bacterial development in animal or vegetable matter. Some are true germicides, capable of de stroying the bacteria, whilst others merely inhibit their growth. The antiseptic method of treating wounds (see SURGERY) was introduced by the late Lord Lister, and was an outcome of Pasteur's germ theory of putrefaction. The standardization of antiseptics has been effected in many instances, and a water solu tion of carbolic acid of a certain fixed strength is now taken as the standard with which other antiseptics are compared. The more important of those in use to-day are carbolic acid, the perchloride and biniodide of mercury, iodoform, formalin, sali cylic acid, etc. Among the more recently introduced antiseptics, chinosol, a yellow substance freely soluble in water, and lvsol, another coal-tar derivative, are much used. But every antiseptic, however good, is more or less toxic and irritating to a wounded surface. Hence antiseptics are nowadays used mainly for the dis infection of instruments, apparatus, the field of operation on the patient's skin and the surgeon's hands, and in cases which are already septic (see SEPsis). Where an incision is to be made into healthy skin or tissues antisepsis has been replaced by asepsis, which relies on keeping free from the invasion of bacteria rather than destroying them when present.
During recent years the study of antiseptics has gone mainly along two lines—to produce more efficient antiseptics for use in the ordinary way by external application, and to elaborate chemical substances which can be injected into the circulation and destroy the infecting microbes. At the same time many studies have been made on the natural antiseptics by which the body rids itself of infection.
These exist in greater or less degree in almost every cell of the human body, as well as in most of the secretions. Mechnikov showed that some cells (phagocytes), and especially the white corpuscles of the blood, could ingest and digest microbes, and Wright discovered that this ingestion or phagocytosis only took place after the microbes had been acted on by the blood fluids. The blood fluids also have a considerable power of destroying or restraining the growth of many pathogenic bacteria (see IMMUNITY). Fleming showed in 1922 that the cells and secretions of the human body have a remarkable antiseptic power toward certain microbes by virtue of their containing a ferment which has been called "Lysozyme." Of all the secretions the tears are the richest in this ferment, and it has been shown that human tears, even when diluted six million times, have a markedly destructive action on some of the microbes found in the air—obviously a natural means of protection against in fection.
Research has been directed to the action of these on the natural defences of the body, and the body cells are, in general, found to be much more susceptible to the action of these chemicals than are bacteria. If an ordinary chem ical antiseptic, e.g., carbolic acid, is added to blood infected with staphylococci or streptococci (the ordinary microbes of suppura tion) the following instructive series of events may be observed. The normal blood itself has such a power of killing these microbes that with a moderate implantation some 95 to 99% are destroyed; but when the concentration of carbolic acid in the blood reaches I in 600 the whole of the natural antiseptic power of the blood is lost and every microbe implanted survives and multiplies. Of course, more concentrated solution of the chemical will, in addi tion to killing the blood cells, inhibit or destroy the bacteria and so exert an antiseptic action, but this is only manifest after the natural defences against infection have been destroyed.
The ideal method of using an antiseptic for the treatment of a bacterial infection is to introduce it into the circulation so that it reaches every portion of the infected focus and destroys the microbes. For ordinary bacterial infections this ideal has not yet been attained, but remarkable advances have been made in this direction in certain infections. In 1910 Ehrlich prepared an organic arsenical product which, when injected into the body, rapidly destroyed the microbe of syphilis, and this product, salvarsan, together with the more recently introduced substances of similar constitution, has revolutionized the treat ment of this disease (see VENEREAL DISEASES). Following Ehr lich, Morgenroth prepared a quinine derivative (Optochin) which had a remarkable affinity for the pneumococcus (the microbe which causes pneumonia), while it had little action on other microbes; but unfortunately this substance had certain toxic qualities which rendered it unsuitable in practice. In some other infections, also, drugs have been found which can destroy the infecting agent without exercising any serious toxic action on the human body ; notable among these are Emetine in amoebic dysen tery (see DYSENTERY), and "Bayer 205" in sleeping sickness. The fact that drugs can be prepared which have a very specific action on one microbe offers some hope that in the near future there will be produced chemicals which will destroy the ordinary disease producing bacteria without damaging the tissues.
Prior to the World War the use of antiseptics in surgery had been largely discarded in favour of aseptic methods which aimed at preventing the access of microbes to the wound. During the war, however, it was found that all the wounds were infected with septic microbes, and many antiseptic methods were employed in the hope of destroying these microbes. Briefly, the results obtained were these : none of the antiseptics was able rapidly to sterilize a wound; most of them were without any evident effect on the bacterial infection; those which have appeared to have some influence on the course of the infection had,• in addition to their "antiseptic" action on the bacteria, a stimulant effect on the infected tissues, and this prob ably contributed largely to their success. The popular pre-war antiseptics, such as carbolic acid, iodine and the salts of mercury, were found to be without effect on the progress of an infection, although outside the body these are powerful bactericidal agents.
Chlorine derivatives obtained great popularity in the form of eusol (hypochlorous acid), sodium hypochlorite (Dakin's fluid) or chloramine-T, a more complicated organic derivative, and this type of antiseptic is still in common use under various trade names. Some of the aniline dyes also are used as antiseptics, and outside the body these are probably the most powerful of all the chemical bactericidal agents. Gentian violet, brilliant green and acriflavine have been largely used, but in all these cases the action on the bacteria 11 slow and the dyes are rapidly absorbed by the tissues and dressings of the wound. Acriflavine differs from al most all other antiseptics in that it has a more powerful action in blood serum than it has in water, and it was hoped from this that it would prove very effective in killing bacteria embedded in the tissues; this hope, however, has not been fulfilled, although the dye still obtains some popularity in the treatment of certain in fections.
Another method of using an antiseptic is to fill the wound with an almost insoluble substance which slowly gives off an antiseptic substance. A good example of this is iodoform, and although this in itself has no power of killing microbes it slowly breaks down in contact with the body fluids and liberates small quantities of iodine, to which the antiseptic action of the iodoform is attributed. This substance, iodoform, used to be very popular in the treat ment of septic infections, but it possesses a very penetrating odour and has been largely given up on this account. In addition to its direct antiseptic action, it possesses, in common with some of the chlorine antiseptics, the power of inducing a large flow of lymph from the wound and so aiding the natural defensive mechanism of the body.
While antiseptics have not been very success ful in killing bacteria in infected tissues in the body, they are invaluable in sterilizing apparatus, instruments and infected mat ter of many kinds outside the body. An infected water supply can be efficiently and economically sterilized by the use of a small quantity of chlorine (see WATER PURIFICATION) ; the infective excreta from cases of typhoid fever and similar diseases can be rendered harmless by treating them with carbolic acid or other similar antiseptic ; catgut for use in surgical operations can only be sterilized by the use of chemical antiseptics, and there are in numerable other ways in which these chemicals fulfil their func tion of destroying bacteria. (A. FL.; W. S. L.-B.) BIBLIOGRAPHY.—H. 0. Nolan, Antiseptics and Germicides; InterBibliography.—H. 0. Nolan, Antiseptics and Germicides; Inter- state M. J., xxiv., p. 809 (19i 7) ; C. Richet and H. Cardot, Des antiseptiques riguliers et irreguliers, C. R. Acad. de Sc., clxv., p.
(1917); H. D. Dakin and E. K. Durham, Handbook of Antiseptics (1917) ; Medical Research Council, London, Special Report No. S7. Studies in Wound Infections (1921) ; S. Rideal and E. K. Rideal, Chemical Disinfection and Sterilization (1921) .
