ANTISEPTICS. Some varieties of vegetable mat ter, and the greater number of the animal products, are liable to a series of spontaneous decompositions, from the re-action of their elements, which constitute the process of putrefaction. The intermixture of cer tain substances counteracts these changes ; renders them more slow, or altogether prevents them : These are named Antiseptics. The power of a number of bodies belonging to this class, has been long known from popular use. The applications of sea-salt, of nitre, of vinegar, and of ardent spirits, to preserve animal sub stances untainted, are among the common practices which have been in use from very remote periods : and the antiseptic quality of a number of aromatic substances, resins and camphor, has led to their employment in em balming, and in some similar processes.
The most extensive series of experiments on the powers of antisepsics, are those which were made a number of years ago, by sir John Pringle, published in the 46th volume of the P hilosonhical Transactions. Though sea-salt is the substance most generally used, perhaps, as an antiseptic, it does not, according to these experiments, derive this from any superiority of power ; for it is inferior to many others ; but is rather preferred, from its communicating no unpleasant taste or other quality to the substances which it preserves. Taking this salt as a standard, and stating its power of preserv ing animal matter, such as flesh, from putrefaction at 1, the comparative powers of other salts are stated in the following table : A number of vegetable substances even exceeded these in antiseptic power. Myrrh, lie supposed to be 30 times more powerful than sea-salt ; several bitters, such as serpentaria, chamomile,or Peruvian bark, he in ferred, exceed it 120 times ; flesh remaining long un tainted, immersed in their infusions : and cam phor, he calculated to be the most powerful perhaps of any antiseptic, its power, compared with that of sea salt, being stated as SOO to 1.
These experiments, however, cannot be regarded as altogether free from fall acy. It was in particular
found, that the different substances did not possess the same comparative antiseptic powers, with regard to dif ferent kinds of animal matter. Much, too, depended on the proportions employed ; as is well shewn by a singular fact, that some substances, such as sea-salt, which in a large proportion resist putrefaction, actually favour it when mixed in a smaller proportion. Some of the gases, especially nitric oxide, are powerful in resisting putrefaction ; and several of the metallic salts, as nitrate of silver, or corrosive muriate of mercury, are used in preserving objects of natural history from the animal kingdom, from their high antiseptic power.
Little satisfactory has as yet been advanced with re gard to the theory of the action of antiseptics. It is sufficiently obvious, that whatever is unfavourable to the exertion of the mutual affinities of the elements of the animal matter, must have a tendency to preserve its composition, and of course must retard putrefaction. Hence the reason, why that process is checked by cold, and also by exsiccation. But it is not easy to explain, on this principle, how many of the substances, which act as antiseptics, operate. There is no obvious opera tion, for example, of sea-salt on animal matter, nor any known chemical agency of it, from which it could-be in ferred, that it would exert any such quality. The power of camphor, and other vegetable antiseptics, has been supposed to be owing to their effluvia being destructive to the ova of insects ;—they probably in part operate by this in preventing the destruction of animal matter ; but this is obviously different from their real antiseptic power, which the experiments of Pringle prove they possess. Those of them which contain tannin, may operate from this principle, entering into combination with the gelatin and albumen of animal matter ; and perhaps, in the greater number of cases, their action is to be ascribed to combinations of this kind being esta blished.