ANTISEPTICS, are the means of preventing those changes in organized matter which are comprehended under the term putrefaction.
All organized substances do not putrefy with equal rapidity, nor under all circum• stances. Decomposition goes on fastest in substances which contain nitrogen, and most slowly in substances which contain carbon; hence animal matters putrefy quickly ; vege table, especially of a woody texture, gradually. The conditions necessary for putrefaction to take place are, tho presence of air, of a certain temperature, and moisture. If any one of these be excluded, the process is prevented. The moisture may either he external, or it may be the fluids of the body itself. The bulk of the animal frame is made up of fluids, which must either be dissipated by heat, ab stracted by some chemical process, or ren dered solid by a very low temperature, if we wish to preserve any animal substance in the state most near that of its natural constitution. The modes of preserving food are either natural or artificial. The natural modes comprehend those which effect this end by abstracting or excluding one or more of the chief agents,—heat, moisture and air; the artificial comprehend those methods of pre paration or mixture which produce some che mical change in the substance.
1st. Abstraction of heat. The presence of heat is essential to the exertion of those che mieal affinities which take place during decom position, or constitute the process ; abstracting it therefore checks or suspends them. Mos articles of food keep better in cold than in warn weather. When the heat has been so con pletely abstracted that the juices are frozen i.e. become solid, the preservation of the sub stance is more effectually accomplished. In deed they may thus be preserved for man:, years, perhaps ages.
On this principle the Russians preserv( their poultry, which they kill in October, and pack in tubs with layers of snow between The markets of St. Petersburg are supplied with veal brought from a great distance in this state, as well as with whole hogs, sheep, and fish. The Canadians preserve their provisions in the same way.
A precaution is necessary in thawing them; for this end, they should always be put into cold water first. Indeed,in the case of persons buried in the snow, recovery is much more likely to be brought about by plunging the individual into cold water, than by placing him in a warm bed.
This method of preserving food is not applicable to vegetables, but when these are frozen they should also be first put into cold water.
2nd. The abstraction of moisture by heat is employed in drying fish and other animal substances, as beef, bacon, Sz.c., though in
these the rapid tendency to putrefaction makes the employment of a certain quantity of salt, &c., necessary, along with the drying, unless the process be carried on with great rapidity, which may be effected by a high temperature and a free circulation of air. Hence in many places, where turf or wood is burnt, hams are hung within the wide kitchen chimney. Dry ing is also employed for the preservation of vegetable substances, such as grain, hay, &c. It is by this means that botanists preserve plants to form a hortus siccus, or herbarium, and many plants are thus preserved for medi cal use, but for this purpose a high tempera ture should never be applied, as it dissipates their active principles.
3rd. The exclusion of sources of oxygen gas constitutes another means of preventing or checking putrefaction ; and as the atmos pheric air is the most common source of oxygen, we shall limit our remarks to the means of excluding it. The effect of such exclusion is very great. Riaumur varnished some eggs, and found that at the end of two years they were yet capable of producing chickens ; and Bomare mentions an instance where three eggs were inclosed within the walls of a church in the Milanese, and when found at the end of 300 years, they had not lost their flavour. Lime-water is the best medium in which to place eggs for long keep ing. But more valuable articles than eggs are preserved by this means ; and in a condition nearly equal to their fresh state. We allude to the method of preserving animal food and vegetables, promulgated by M. Appert. This consists in boiling the articles (if meat, the bones must be first taken out) to nearly as great a degree as if intended for immediate consumption ; they are then put into jars or tin canisters, which must be completely filled with a broth or jelly prepared from portions of the same meat. The jars are then corked and covered with a luting, and the canisters carefully soldered down. After this, they are placed in a boiler of cold water, to which heat is applied till the water boils, and the boiling of which is continued for an hour; the fire must then be instantly extinguished, and the water soon drawn off, but the boiler must not be uncovered, or the bottles taken out, for one or two hours after. By this method meat has been kept sound and well-flavoured for six years and upwards, and has been sent to all parts of the globe. The process of ex hausting the air from the vessel which con tains the substance to be preserved, and then effectually excluding the atmosphere is a me thod now frequently used.