of being resolved into the same principle as those of the latter. Thus, by repeated distillations, we obtain from animal substances, water, oil, air, an easy destructible salt, and charcoal. These secondary principles, are, by farther processes, at length resoluble into the same proximate principles which we find in vegetables, viz., air, earth, and water, and the principle of inflammability.

But though the principles of vegetable and animal substances are fundamentally the same, yet these principles are combined in a very different manner. It is exceedingly rare that animal substances are capable of the vinous or acetous fermentation, and the putrefactive, into which they run remarkably fast, is also different in some particulars from the putrefaction of vegetables. The smell is much more offensive in the putrefaction of animal than of vegetable substances. The putrefaction of urine, is, indeed, accompanied with a peculiar fetor, by no means so intolerable as that of other animal matters; this is, probably, owing to the pungency of the volatile alkali, and also to the urine containing less inflammatory matter than the blood and other fluids. When analysed by a destructive heat, animals afford products very different from those of vegetables; the empyreumatic oil has a particular and much more fœtid odour, and the volatile salt instead of being an acid, found as it is in most vegetables, is found in animals to be a volatile alkali.

Chemists have spoken of an acid procurable from animal substances, and indeed, certain parts of animal bodies are found to yield a salt of this kind; but it by no means is the case with animal substances in general; and though the proofs to the contrary were even conclusive, it is confessedly in so small a quantity as not

to deserve any particular regard. In some animals, however, an acid exists, uncombined and ready formed in their bodies. This is particularly manifest in some insects, especially ants, from which an acid has been procured by boiling them in water.

The solid parts of animal bodies, as the muscles, teguments, tendons, cartilages, and even the bones, when boiled with water, give a gelatinous matter or glue, resembling the vegetable gums, but much more adhesive. We must, however, except the horny parts and the hair, which seem to be little soluble either in water or in the liquors of the stomach. The acids, the alkalies, and quick-lime, are also found to be powerful solvents of animal matter. It is from the solid parts that the greatest quantity of volatile alkali is obtained; it arises along with a very fœtid empyreumatic oil, from which it is in some measure separated by repeated rectifications. This salt is partly in a fluid, and partly in a solid state, and from its having been formerly prepared in the greatest quantity from the horns of the stag, it has been called salt, or spirits of hartshorn. Volatile alkali, however, is procurable from all animals, and from almost every part of an animal, except the fat. Though we are sometimes able to procure the fixed alkali from an animal cinder, yet it is probable that this salt did not make any part of the living animal, but rather proceeded from the introduction of saline matter, incapable of being assimilated by the functions of the living

creature.

In speaking of the fluid parts of animals, we should first examine the general fluid from whence the rest are secreted. The blood, which at first sight, appears to be a homogenous fluid, is composed of several parts, easily separable from each other, and which the

microscope can even perceive in its uncoagulated state. On allowing it to stand at rest and to be exposed to the air, it separated into what are called the crassamentum and the serum. The crassamentum consists chiefly of the red globules, joined together by another substance, called the coagulable lymph; the chemical properties of these globules are not as yet understood, but they seem to contain the greatest quantity of iron found in the blood.

The serum is a yellowish subviscid liquor, having little sensible taste or smell; at a heat of 160 Farenheit's thermometer it is converted into a jelly. This coagulation of the serum is also owing to its containing a matter of the same nature with that of the crassamentum, viz., the coagulable lymph; whatever then coagulates animal blood, produces that effect on this concrescible part.

Several causes, and many different substances, are capable of effecting this coagulation, such as contact of air, heat, alcohol, mineral acids, and their combinations with earths, as alum, and some of the metallic salts. The more perfect neutral salts are found to prevent the coagulation, such as common salt and nitre.

Of the fluids secreted from the blood, there are a great variety in men and other animals.

The excrementitious and redundant fluids are those which afford, in general, the greatest quantity of volatile alkali, and empyreumatic oil. There are also some of the secreted fluids, which, on a chemical analysis, yield products in some degree peculiar to themselves. Of this kind is the urine, which is found to contain in the greatest abundance the noted salt formed from the phosporic acid and volatile alkali. The fat, too, has been said to differ from other animal matters in yielding, by distillation, a strong acid, but

no volatile alkali. There is also much variety in the quantity and state of the combination of the saline and other matters in different secreted fluids.

Animal oils and fats, like the gross oil of vegetables, are not of themselves soluble, either in water or vinous spirit, but they may be united with water by the intervention of gum or mucilage. Most of them may be changed into soap by fixed alkaline salts, and may thus be rendered miscible with spirit as well as water.

The oderous matter of some oderiferous animal substances, as musk, civet, castor, is, as well as essential oil, soluble in spirit of wine, and volatile in the heat of boiling water.

It is said that an actual essential oil has been obtained from castor in a very small quantity, but of an exceedingly strong diffusive smell. The blistering matter of cantharides, and those parts of sundry animal substances in which their peculiar taste resides, are dissolved by rectified spirit, and seem to have some analogy with any gummy resins.

The gelatinous principle of animals, like the gum of vegetables, dissolves in water, but not in spirit or in oils; like gums also, it renders oils and fats miscible with water into a milky colour. Some insects, particularly the ant, are found to contain an acid juice, which approaches nearly to the nature of vegetable acid. There are, however, sundry animal juices which differ greatly, even in these general kinds of properties, from the corresponding ones of vegetables. Thus, animal serum, which appears analagous to vegetable gummy juices, has this remarkable difference, that though it mingles uniformly with cold or warm water, yet, on considerably heating the mixture, the animal matters separate from the watery fluid, and concretes into a solid mass.

Some have been of opinion, that the heat of the animal body in certain diseases might rise to such a degree as to produce this dangerous or mortal concretion of the serous humours, but the heat requisite for this effect is greater than it appears capable of sustaining. The soft and fluids parts of animals are strongly disposed to run into putrefaction; they putrefy much sooner than vegetable matter, and when corrupted, prove more offensive.

This process takes place, in some degree, in the bodies of living animals, as often as the juices stagnate long, or are prevented by an obstruction of the natural emunctories from throwing off their more volatile and corruptible parts. During putrefaction, a quantity of air is generated, all the humours become gradually thinner, and the fibrous parts more lax and tender; hence, the tympany, which succeeds the induration of any of the viscera, or the imprudent suppression of dysentries by astringents, and the weakness and laxity of vessels observed in the scurvy, &c. The crassamentum of human blood, as well as that of quadrupeds, change by putrefaction into a dark livid colour, a few drops of which tinge the serum with a tawny hue, like the ichor of sores and dysenteric fluxes, as also the white of the eye, the saliva, the serum of blood drawn from a vein, and the liquid that oozes from a blister in the scurvy, and in the advanced state of malignant fevers.

The putrid crassamentum changes a large quantity of recent urine to a flame-coloured water, so common in fevers and in the scurvy. The mixture, after standing an hour or two, gathers a cloud resembling what is seen in the crude water of acute distempers, with some oily matter on the surface like the scum which floats on scorbutic urine. The serum of the