PUTREFACTION is the natural process of decomposition, by which the elements of organic matter are made to enter into a different state of combination, and by which new products are formed.

Putrefaction has been generally considered as a species of fermentation, which has been divided into three kinds, the vinous, the acetous, and the putrefactive. The first is so termed, because during its progress spirit of wine is formed; the second, because acetum or vinegar is proddeed; and the last, because by it the substance runs into putrefaction.

All animal and vegetable matter is liable to undergo putrefaction; certain circumstances,, however, are necessary for the commencement and continuance of the process, as the presence of moisture and a due degree of heat.

With regard to the putrefaction of vegetable bodies, the substance first becomes mouldy, it then emits an offensive odour, and in the course of time is in· a great measure consumed. That moisture is necessary seems evident; for if the vegetable be cautiously dried by the application of heat, it may be preserved for almost any length of time. Hence the heat at which it must be kept, so as to make it putrefy, must not be such as will expel the moisture. On the contrary, when the temperature is low, the putrefactive process is put a stop to.

The admission of air also favours putrefaction, by allowing the escape of the volatile products. Many vegetable substances, however, particularly those that contain a large amount of carbon, are not entirely consumed by putrefaction; there is left a substance called vegetable mould, which does not putrefy when excluded from the air, but soon does so when exposed to it.

Vegetable mould constitutes apart of the soil, and contributes to vegetation, provided it be exposed to the atmosphere; hence the necessity of turning up the soil to cause the putrefaction to go on, by which it is supposed the mould, during its decay, becomes soluble, so that it is easily taken up by plants, and thus affords them nourishment. But when this is not done, more particularly when the mould is in large quantity, it accumulates, and hence the origin of peat and morass.

Animal matter is also liable to putrefaction; indeed it decays more easily than vegetables, provided it be kept at the requisite temperature, which is between forty and eighty degrees; the nearer to the latter the better; and if below thirty-two it ceases. Moisture is also necessary, and the freer the admission of air, the more rapid is the decomposition.

The first appearance of putrefaction is a change of colour and of consistence; the matter becomes paler and softer, emits a disagreeable smell, and at the same time evolves gaseous bodies, the nature of which depends on that of the animal substance; but it in general consists of carbonic acid, sulphuretted hydrogen, and volatile alkali, the disengagement of which ceases in the course of time, and a dry hard mass remains, containing the fixed principles of the animal kingdom.

When, instead of being exposed freely to air, the matter is buried, the putrefaction goes on more slowly, especially when the earth is dry, because the moisture from the animal matter is extracted. When the air is completely excluded, the substance is not entirely destroyed; the elements, by their new state of combination, form a peculiar principle resembling spermaceti, which has been called adipocere, from its properties being intermediate to those of fat and of wax.

Various means are resorted to for retarding or preventing putrefaction, both of animal and vegetable matter. Perhaps the most efficacious is cold, which is supposed to act by causing the congelation of the moisture, and thus preventing the elements from entering into new states of combination. It is well known that vegetables and butchermeat, wlíen put into snow, may be preserved for almost any length of time; and hence the common practice of sending fish to a distance packed in ice; whilst in the northern regions the inhabitants are in the custom of laying up a store of provisions surrounded by snow, by which they are kept fresh till required.

Depriving organic matter of moisture is another mode of retarding putrefaction; and hence it is that, when the sub [7:18:743]stance is exposed cautiously to heat, by which the moisture is expelled, the putrefactive process is prevented. Hence the practice of drying fish; and in some countries it is customary to cut flesh into thin slices and dry it, in which state it is kept until it be required.

As exposure to air promotes putrefaction, exclusion from it retards it; and this affords another method of preserving animal and vegetable matter. Hence the custom of rubbing eggs over with butter, and also of keeping them in lime-water. Butcher-meat, also, well packed in barrels, from which the air is completely excluded, may be kept fresh for a considerable time, and more particularly if the meat be par-boiled before it is packed. Strong soups, after being cooled, and of course congealed, are preserved during long voyages, by’ being put into earthen dishes, and in general covered with a layer of melted fat, and afterwards secured from the air by bladder or tinfoil. In many cases the meat is packed into tin boxes, the lids of which are afterwards soldered down so as to exclude the air. In this way meat has been taken to India and returned to this country as fresh as when put into the packages.

There are many substances which retard, indeed prevent putrefaction, and some of them, it is supposed, act by absorbing the moisture. The most powerful of these antiseptics is sea-salt, which, it is well known, is used largely in preserving meat, fish, butter, &c. Another substance which acts powerfully is pyroligneous acid; but it is generally allowed that it acts not by the acid which it contains, but by a peculiar principle formed during its formation, and in all probability similar to, if not the same as, that now called creosote ; indeed it is also supposed that during the process of smoking, to which fish, and sometimes also meat, are subjected, the same principle is formed, and that it is this which acts in preventing putrefaction.

Sugar, it is well known, is also a powerful antiseptic, and hence its use in making preserves, &c.; so also is spirit of wine, and the volatile oils, as turpentine, which are much employed in preserving anatomical preparations.

Sir John Pringle made experiments to determine the powers of certain substances in promoting or preventing putrefaction. From these experiments he formed the following table, showing the relative antiseptic powers of the saline substances mentioned. Having found that two drams of beef put into a phial with two ounces of water, and placed in a heat equal to 90° of Fahrenheit’s thermometer, became putrid in fourteen hours, and that sixty grains of sea-salt preserved a similar mixture of beef and water more than thirty hours, he made the antiseptic power of the sea-salt a standard, to whichTιe compared the powers of the other salts. The algebraic character + signifies that the substance to which it is annexed had a greater antiseptic power than is expressed by the numbers.
[table]

The quantities of spiritus Minderen and of the saline mixture were such, that each of them contained as much alkaline salt as the other did neutral salts.

Myrrh, aloes, asafoetida, and terra Japonica, were found to have an antiseptic power thirty times greater than the standard. Gum ammoniacum and sagapenum showed little antiseptic power.

Of all resinous substances, camphor was found to resist putrefaction most powerfully. Sir John Pringle believes that its antiseptic power is three hundred times greater than that of sea-salt.

Chamomile flowers, Virginian snake-root, pepper, ginger, saffron, contrayerva root, and galls, were found to be twelve times more antiseptic than sea-salt.

Infusions of large quantities of mint, angelica, groundivy, green tea, red roses, common wormwood, mustard, and horse-radish, and also decoctions of poppy-heads, were more antiseptic than sea-salt.

Decoctions of wheat, barley, and other farinaceous grains, checked the putrefaction by becoming sour.

Chalks and other absorbent powders accelerated the putrefaction, and resolved meat into a perfect mucus. The same powders prevented an infusion of farinaceous grains from becoming mucilaginous and sour.

One dram of sea-salt was found to preserve two drams of fresh beef in two ounces of water above thirty hours un corrupted, in a heat equal to that of the human body, or above twenty hours longer than meat is preserved in water without salt; but half a dram of salt did not preserve it more than two hours longer than pure water. Twenty-five grains of salt had little or no antiseptic quality. Twenty grains, fifteen grains, but especially ten grains only, of seasalt, were found to accelerate and heighten the putrefaction of two drams of flesh. These small quantities of sea-salt also softened the flesh more than pure water.

The same learned and ingenious physician made experiments to discover the effects of mixing vegetable with animal matters.

Two drams of raw beef, as much bread, and an ounce of water, being beaten to the consistencfe of pap, and exposed to 90° of heat according to Fahrenheit’s thermometer, began to ferment in a few hours, and continued in fermentation during two days. When it began to ferment and swell, the putrefaction had commenced; and in a few hours afterwards the smell was offensive. Next day the putrid smell ceased, and an acid taste and smell succeeded. Fresh alimentary vegetables, as spinach, asparagus, scurvy-grass, produced similar effects to bread on flesh, but in a weaker degree. From several other experiments, he found that animal substances excite the fermentation of vegetable substances, and that the latter substances correct the putrescency of the former.

By adding saliva to a similar mixture of flesh, bread, and water, the fermentation w∙as retarded, moderated, but rendered of twice the usual duration; and the acid at last produced was weaker than when no saliva was used.

By adding an oily substance to the common mixture of flesh, bread, and water, a stronger fermentation was produced, which could not be moderated by the quantity of saliva used in the following experiment, till some fixed alkaline salt was added; which salt was found, without saliva, to stop suddenly very high fermentations.

Sir John Pringle did not find that small quantities of the following salts, sal-ammoniae, nitre, vitriolated tartar, sal diureticus, salt of hartshorn, salt of wormwood, were septic, as small quantities of sea-salt were. Sugar was found to resist putrefaction at first, as other salts do, and also to check the putrefaction after it had begun by its own fermentative quality, like bread and other fermentative vegetables. Limewater made some small resistance to putrefaction.

Port wine, small beer, infusions of bitter vegetables, of bark, and the juice of antiscorbutic plants, retarded the fermentation of mixtures of flesh and bread; but an unstrained decoction of bark considerably increased that fermentation.
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Crab-eyes accelerated and increased the fermentation of a mixture of flesh and bread. Lime-water neither retarded nor hastened the fermentation of such a mixture; but when the fermentation ceased, the liquor was neither putrid nor acid, but smelt agreeably. Flesh pounded in a mortar was found to ferment sooner than that which had not been bruised. The tough inflammatory crust of blood was found to be most putrescent; next to which the crassamentum, or red coagulated mass; and lastly the serum.

Dr Mackbride’s experiments confirm many of those above related, especially such as show that the fermentation of vegetable substances is increased by a mixture of animal or putrescent matter; that the putrescency of the latter is corrected by the fermentative quality of the former; and that the putrefaction and fermentation of mixtures of animal and vegetable substances were accelerated by additions of absorbent earths and of Peruvian bark. He also found, that although nnburned calcareous earths were septic, quicklime and lime-water prevented putrefaction, but that they destroyed or dissolved the texture of flesh.

The experiments of the author of the Essai pour servir a l’Histoire de la Putréfaction showed that metallic salts, resinous powders, extracts of bark, and opium, were very powerfully antiseptic; and that salts with earthy bases were less antiseptic than any other salts.