is the natural process by which organized bodies etc. dissolved, and reduced to what may be called their original elements.

Putrefaction differs from chemical solution; because in the latter, the dissolved bodies are kept in their state of solution by being combined with a certain agent from which they cannot easily be separated; but in putrefaction, the agent which dissolves the body appears not to combine with it in any manner of way, but merely to separate the parts from each other. It differs also from the resolution of bodies by distillation with violent fire; because, in distillation, new and permanent compounds are formed, but by putrefaction everything seems to be resolved into substances much more simple and indestructible than those which are the result of any chemical process.

The bodies most liable to putrefaction are those of animals and vegetables, especially when full of juices. Stones, though by the action of the weather they will moulder into dust, yet seem not to be subject to anything like a real putrefaction, as they are not resolved into any other substance than sand, or small dust, which still preserves its lapidaceous nature. In like manner, vegetables of any kind, when deprived of their juices by drying, may be preserved for many ages without being subjected to anything like a putrefactive process. The same holds good with respect to animals; the parts of which, by simple drying, may be preserved in a sound state for a much longer time than they could be without the previous exhalation of their juices.

Putrefaction is generally allowed to be a kind of fermentation, or rather to be the last stage of that process; which beginning with the vinous fermentation, goes on through the acetous, to the stage of putridity, where it stops. It is argued, however, and seemingly not without a great deal of reason, that if putrefaction be a fermentation, it must necessarily be a kind differing from either the vinous or acetous; since we frequently observe that it takes place where neither the vinous nor the acetous stages have gone before; of consequence, it must be, in some cases at least, entirely independent of and unconnected with them. In several other respects it differs so much from these processes, that it seems in some degree doubtful whether it can with propriety be called a fermentation or not. Both the vinous and acetous fermentations are attended with a considerable degree of heat; but in the putrefaction of animal matters especially, the heat is for the most part so inconsiderable, that we cannot be certain whether there is any degree of it or not produced by the process. In cases, indeed, where the quantity of corrupting animal matter is very great, some heat may be perceived: and accordingly Dr Monro tells us, that he was sensible of heat on thrusting his hand into the flesh of a dead and corrupting whale. But the most remarkable difference between the putrefactive fermentation and that of the vinous and acetous kinds is, that the end of both these processes is to produce a new and permanent compound; but that of the putrefactive process is not to produce any new form, but to destroy, and resolve one which already exists into the original principles from which all things seem to proceed. Thus the vinous fermentation produces ardent spirits; the acetous, vinegar: but putrefaction produces nothing but earth, and some effluvia, which, though most disagreeable, and even poisonous to the human body, yet, being imbibed by the earth and vegetable creation, give life to a new race of beings. It is commonly supposed, indeed, that volatile alkali is a production of the putrefactive process: but this seems liable to dispute. The vapour of pure volatile alkali is not hurtful to the human frame, but that of putrefying substances is exceedingly so; and, excepting in the case of urine, the generation of volatile alkali in putrid substances is very equivocal. This substance, which produces more alkali than any other, is much less offensive by its putrid fetor than others; and all animal substances produce a volatile alkali on being exposed to the action of fire, of quicklime, or of alkaline salts. In these cases the volatile alkali is not supposed to be produced by the quicklime or fixed salt, but only to be extricated from a kind of ammoniacal salt pre-existing in the animal matters; the probability is the same in the other case, viz. that volatile alkali is not produced, but only extricated, from these substances by putrefaction.

The only thing in which the putrefactive fermentation agrees with the other kinds is, that in all the three there is an extrication of fixed air. In the putrefactive process, it has been thought that this escape of the fixed air deprives the body of its cohesion; and Dr Macbride has written a treatise, in which he endeavours to prove that fixed air is the very power of cohesion itself, and that all bodies when deprived of their fixed air entirely lose their cohesion. According to this hypothesis, the cause of putrefaction is the escape of fixed air; but it is impossible to give a reason why fixed air, after having for long remained in a body, and preserved its cohesion, should of a sudden begin to fly off without being acted upon by something else. To a similar objection the hypothesis of those is liable, who suppose putrefaction to be occasioned by the escape of phlogiston; for phlogiston is now known to be a chimera: and though it were a reality, it would not fly off without something to carry it off, any more than fixed air. Animalcules have been thought to be the cause of putrefaction: but if animal substances are covered so as to exclude the access of flies or other insects, no such animalcules are to be discovered though putrefaction has taken place; and indeed it requires little proof to convince us, that animals are produced in corrupted bodies only because such substances prove a proper nidus for the eggs of the parent insects. To understand the true cause of putrefaction, we must take notice of the circumstances in which the process goes on most rapidly. These are, heat, a little moisture, and confined air. Extreme cold prevents putrefaction, as well as perfect dryness; and a free circulation of air carries off the putrid effluvia; a stagnation of which seems to be necessary for carrying on the process. It seems also to hold pretty generally, that putrefying bodies swell and become specifically lighter; for which reason the carcases of dead animals, after having sunk in water, rise to the top and float. This last phenomenon, as has been observed under the article BLOOD, No. 29, shows that these bodies have received a certain quantity of an elastic principle from the air, which thus swells them up to such a size. It may be said indeed, that this increase of size in putrefying bodies is owing only to the extrication of air within themselves; but this amounts to the same thing; for the air which exists internally in the body of any animal, is entirely divested of elasticity while it remains there, and only shows its elastic properties upon being extricated. The elastic principle which combines with the air fixed in the animal substance, therefore, must come from the external atmosphere; and consequently the agent in putrefaction must be the elastic principle of the atmosphere itself, probably the same with elementary fire.

But, granting this to be true, it is difficult to show why putrefaction should not take place in a living body as well as in a dead one; seeing the one is as much exposed to the action of the air as the other. This difficulty, however, is not peculiar to the present hypothesis; but will equally occur whatever we may suppose the cause of putrefaction to be. The difficulty seems to be a little cleared up by Dr Priestley, who shows, that, by means of respiration, the body is freed from many noxious effluvia which would undoubtedly destroy it; and by the retention of which, he thinks, a living body would putrefy as soon as a dead one. The way in which respiration prevents the putrefaction of the body, is evidently the same with that in which the wind prevents fish or flesh hung up in it from becoming putrid. The constant inspiration of the air is like a stream of that element continually blown upon the body, and that not only upon its surface, but into it; by which means putrefaction is prevented in those parts that are most liable to become putrid. On the other hand, the elastic principle received from the air by the blood* by invigorating the powers of life, quickening the circulation, and increasing perspiration, enables the body to expel noxious particles from other parts of the body which cannot conveniently be expelled by the lungs.

This leads us to consider the reason why a free exposure to the air prevents the coming on of putrefaction, or why the confining of the putrid effluvia should be so necessary to this process. Here it will be proper to recollect, that putrefaction is a simple resolution of the body into earth, air, &c., of which it seems originally to have been composed. This resolution is evidently performed by an expansive power seemingly situated in every particle of the body. In consequence of this principle, the body first swells, then bursts, flies off in vapour, and its particles fall asunder from each other. The action of the putrefactive process, then, is analogous to that of fire, since these are the very properties of fire, and the very effects which follow the action of fire upon any combustible body. It is therefore exceedingly probable, that the agent in the air, which we have all along considered as the cause of putrefaction, is no other than fire itself; that is, the ethereal fluid expanding itself everywhere, as from a centre to a circumference. The force of the fluid, indeed, is much less in putrefaction than in actual ignition; and therefore the effects also take place in a much smaller degree, and require a much longer time: nevertheless, the same circumstances that are necessary for keeping up the action of fire, are also necessary for keeping up the putrefactive process. One of these is a free access of air, yet without too violent a blast; for as fire cannot burn without air, neither can it endure too much of it: thus a candle goes out if put under a receiver, and the air exhausted; and it will do the same if we blow violently upon it. In like manner, putrefaction requires a certain quantity of air, much less indeed than fire: and as it requires less to support it, so it can also endure much less air than fire; for a stream of air which would not put out a fire, will effectually prevent putrefaction. The cause of this in both is the same. Fire cannot burn because the vapour is carried off too fast; and thus the latent heat, which ought to support the flame, is entirely dissipated. In like manner putrefaction is as certainly attended with an emission of azotic gas as fire is with an emission of flame. These gases contain a great quantity of latent heat, or of the expansive principle already mentioned; and if these are carried off with greater rapidity than the heat of the atmosphere can produce them, the consequence must be, that an opposite principle to that which produces putrefaction, namely, a principle of cold, or condensation, instead of expansion, must take place, and the body cannot putrefy. That this must be the case, is evident from the property which all evaporations have of producing cold; and it is well known that a brisk current of air promotes evaporation to a great degree. Hence also the reason is evident why bodies are preserved uncorrupted by cold; for thus the action of the expansive principle is totally overcome and suspended, so that none of its effects can be perceived.

Thus we may say, that one reason why an animal body does not putrefy while alive, is its ventilation, as we may call it, by respiration; and another is, the continual accession of new particles, less disposed to putrefy, than itself, by the food and drink which is constantly taken in. But if either of these ways of preventing the commencement of this process are omitted, then putrefaction will take place as well in a living as in a dead body. Of the truth of this last fact we have innumerable instances. When air is infected with the putrid effluvia of marshes, and thus the natural effluvia are not carried off from the human body; but, on the contrary, some enter into it which are not natural to it, the most putrid diseases are produced. The same thing happens from the putrid effluvia of dead bodies. Of this we have a remarkable instance in the fever which took place in Germany in the war of 1755: one reason of which is said to have been an infection of the air by the vast numbers of people killed in battle, to which was added a calm in the atmosphere for a long time; the putrid effluvia being by this prevented from flying off. When Mr Howell with 145 others were imprisoned in the black-hole at Calcutta, after passing 167. Putrefaction.

a night in that dismal habitation, he found himself in a high putrid fever. When sailors in long voyages are obliged to feed upon putrid aliments; when, through stormy weather, they are much exposed to wet; in the one case the putrefactive effluvia being kept from flying off, and in the other a greater quantity being thrown into the body than what it naturally contains, the febrile, malignant fevers, &c. make their appearance (a). Neither can these diseases be removed without removing every one of the causes just now mentioned: for as putrid diseases will be the consequence of confined air, nastiness, &c. though the provisions be ever so good; so on the other hand, if the provisions be bad, the best air, and most exact cleanliness, nay, the best medicines in the world, will be of no service; as hath been often observed in the febrile.

From this account of the nature, cause, and method of preventing putrefaction by means of a current of air, we may easily see the reason why it does not take place in some other cases also. Bodies will not putrefy in vacuo, because there the atmosphere has not access to impart its elastic principle; and though in the vacuum itself the principle we speak of does undoubtedly exist, yet its action there is by far too weak to decompose the structure of an animal body. In extreme cold, the reason why putrefaction does not take place, has been already shown. If the heat is extremely great, the process of ignition or burning takes place instead of putrefaction. If the body is very dry, putrefaction cannot take place, because the texture is too firm to be decomposed by the weak action of the elastic principle. Putrefaction may also be prevented by the addition of certain substances; but they are all of them such as either harden the texture of the body, and thus render it proof against the action of the elastic fluid, or, by dissolving its texture entirely, bring it into a state similar to what it would be brought by the utmost power of putrefaction, so that the process cannot then take place. Thus various kinds of salts and acids harden the texture of animal substances, and thus are successfully used as antiseptics. The same thing may be said of ardent spirits; while oils and gums of various kinds prove antiseptic by a total exclusion of air, which is necessary in some degree for carrying on the process of putrefaction. Many vegetables, by the astringent qualities they possess, harden the texture of animal substances, and thus prove powerfully antiseptic; while, on the other hand, fixed alkaline salts, quicklime, and caustic volatile alkali, though they prevent putrefaction, yet they do it by dissolving the substances in such a manner that putrefaction could do no more though it had exerted its utmost force. There is only one or other antiseptic substance whose effects deserve to be considered, and that is sugar. This, though neither acid nor alkaline, is yet one of the most effectual means of preventing putrefaction: and this seems to be owing to its great tendency to run into the vinous fermentation, which is totally inconsistent with that of putrefaction; and this tendency is so great, that it can scarce be counteracted, by the tendency of animal substances to putrefy in any circumstances whatever.

Some kinds of air are remarkably antiseptic, though this subject has not been so fully inquired into as could be wished. The most powerful of them in this respect is the nitrous air; next to it, is fixed air; but the powers of the other airs are not so well known. It is probable that the antiseptic properties of fixed and nitrous air, are owing to their quality of extinguishing fire, or at least that the principle is the same; but, till the nature of these two kinds of air are better known, little can be said with certainty on the subject.

Sir John Pringle has made experiments to determine the powers of certain substances to promote or to prevent putrefaction. From these experiments he has formed the following Table, showing the relative antiseptic powers of the saline substances mentioned. Having found that two drams of beef put in a phial with two ounces of water, and placed in a heat equal to 95° of Fahrenheit's

(a) This aeriform fluid, which is exhaled from animal bodies in a state of putrefaction, acts at certain times more powerfully than at others, and is indeed in one stage of the process infinitely more noxious than any other elastic fluid yet discovered. In the Gentleman's Magazine for August 1788, Dr St John, informs us, that he knew a gentleman who, by slightly touching the intestines of a human body beginning to liberate this corrosive gas, was affected with a violent inflammation, which in a very short space of time extended up almost the entire length of his arm, producing an extensive ulcer of the most foul and frightful appearance, which continued for several months, and reduced him to a miserable state of emaciation. The same writer mentions a celebrated professor who was attacked with a violent inflammation of the nerves and fauces, from which he with difficulty recovered, merely by stooping for an instant over a body which was beginning to give forth this deleterious fluid. Hence he infers, that the same gas modified or mixed, or united with others, may be the occasion of the plague, which has so often threatened to annihilate the human species. It is happy, however, for mankind that this particular stage of putrefaction continues but for a few hours; and, what may appear very remarkable, this destructive gas is not very disagreeable in smell, and has nothing of that abominable and loathsome fetor produced by dead bodies in a less dangerous state of corruption; but has a certain smell totally peculiar to itself, by which it may be instantly discovered by any one that ever smelled it before. This is an object very worthy the attention of physicians: it is both extremely interesting, and very little known; but at the same time it is a study in the highest degree unpleasant, from the detestable smell and nastiness which attend the putrefaction of animal bodies; and a man must be armed with uncommon philanthropy and resolution to attempt it.

Dr St John thinks it probable that there is a rapid fixation of the basis of vital air in dead bodies at a certain state of putrefaction, on account of the luminous appearance which they sometimes make, and which exists but for a few hours: but whether this luminous appearance takes place in every body, or whether it precedes or follows the exhalations of the corrosive gas above mentioned, he had not, when he wrote his paper, been able to discover. Fahrenheit's thermometer, became putrid in 14 hours, and that 60 grains of sea-salt preserved a similar mixture of beef and water more than 30 hours, he made the antiseptic power of the sea-salt a standard, to which he 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:

| Substance | Power | |---------------------------|-------| | Sea-salt, or the standard | 1 | | Sal-gem | 1+ | | Vitriolated tartar | 2 | | Spiritus Mindereri | 2 | | Soluble tartar | 2 | | Sal diureticus | 2+ | | Crude sal ammoniac | 3 | | Saline mixture | 3 | | Nitre | 4+ | | Salt of hartshorn | 4+ | | Salt of wormwood | 4+ | | Borax | 12 | | Salt of amber | 20 | | Alum | 30 |

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

Myrrh, aloes, afaestida, and terra Japonica, were found to have an antiseptic power 30 times greater than the standard. Gum ammoniacum and lagapenum showed little antiseptic power.

Of all refractive substances, camphor was found to resist putrefaction most powerfully. Sir John Pringle believes that its antiseptic power is 300 times greater than that of sea-salt.

Chamomile flowers, Virginian snake-root, pepper, ginger, saffron, contrayerva root, and galls, were found to be 12 times more antiseptic than sea-salt.

Infusions of large quantities of mint, angelica, ground-ivy, green tea, red-robes, 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 30 hours, uncorrupted, in a heat equal to that of the human body, or above 20 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, 15 grains, but especially 10 grains only of sea-salt, were found to accelerate and heighten the putrefaction of two drams of flesh. These small quantities of sea salt did also soften 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 beat to the consistence 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 begun; 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, fcurvy-grafs, produced similar effects as 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 putrefaction of the former.

By adding saliva to a similar mixture of flesh, bread, and water, the fermentation was retarded, moderated, but rendered twice the usual duration, and the acid produced at last 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 former experiment, till some fixed alkaline salt was added; which salt was found, without saliva, to stop suddenly very high fermentations.

He did not find that small quantities of the following salts, sal ammoniac, 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.

Lime-water 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.

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 putrefied; next to which the crustamentum, or red coagulated mass; and lastly the serum.

Dr Macbride's experiments confirm many of those above related, especially those which show that the fermentation of vegetable substances is increased by a mixture of animal or putrefied matter; that the putrefaction 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 unburnt 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 à l'Histoire de la Putrefaction, show that metallic salts, Putrefaction

Pyanephia.

Pyanephia.