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materials:-first, a peculiar aroma, or odour, of which every one must be sensible who has been present at a slaughter-house on cutting up the fresh bodies of oxen; secondly, fibrine, or fibrous matter; thirdly, uncoagulable matter, but no gelatin, which is a subsequent secretion; fourthly, albumen; fifthly, red-colouring matter; sixthly, iron; seventhly, sulphur; eighthly, soda; and, lastly, water. The proportion of these parts vary almost infinitely, according to the age, temperament, and manner of living; each of these having a character that essentially belongs to it, with particular shades that are often difficult to be laid hold of.

Of these component parts, the most extraordinary are the red-colouring matter, the iron, and the sulphur; nor are we by any means acquainted with the mode by which they obtain an existence in the blood. I have already had occasion to observe, that albumen and fibrine are substances formed by the action of the living principle out of the common materials of the food, and that it is probable the lime found in the bones and other parts is produced in the same manner. Whether the iron and sulphur that are traced in the blood have a similar origin, or exist in the different articles of our diet, and are merely separated from the other materials with which they are combined, is a physical problem that yet remains to be solved. It should be observed, however, that the sulphur does not exist in a free state even in the blood itself, but is only a component part of its albumen. Considering the universality of these substances in the blood, and the uniformity of their proportion in similar ages, temperaments, and habits, whatever be the soil on which we reside; that those who live in a country in which these minerals are scarcely to be traced have not less, while those who live in a country that overflows with them have not more; it is perhaps most rational to conclude, that they are generated in the laboratory of the animal system itself, by the all-controlling influence of the living principle.

The exact proportion of sulphur contained in the system has been less accurately ascertained than that of the iron, which last in an adult, the weight of whose blood may be estimated at 28lbs., ought usually to amount to seventy scruples, or about three ounces: and hence the blood of about forty men contains iron enough to make a good ploughshare, and might easily have its iron extracted from it, be reduced to a metallic state, and manufactured into such an instrument.

Iron is seldom found except in the red particles of the blood;† and it has hence been supposed by the French chemists to be the colouring material itself. The process of respiration, according to the theory of Lavoisier and Fourcroy, is a direct process of combustion, in which the animal system finds the carbon, and the atmosphere the oxygen and caloric; and in consequence of the sensible heat which is set at liberty during the combustion, the iron of the blood is converted into a red oxide, and hence necessarily becomes a pigment.

But it is impossible to ascribe the red colour to this principle: for, first, we are by no means certain that the air communicates any such substance as caloric to the blood; and, secondly, let the sensible heat of the blood arise from whatever quarter it may, it can never be sufficiently augmented by the most violent degree, either of local or general inflammation, to convert the iron of the blood into a red oxide, which, indeed, is never produced without rapid combustion, flame, and intense heat. And hence, Sir Humphry Davy conjectures the carbon itself of the blood to be the real colouring material, and to be separated from the oxygen, with which it is necessarily united to constitute

* Blumenbach states the proportion in an adult and healthy man to be as 1 to 5 of the entire weight of the body. By experiments on the water-newt (lacerta palustris), he found the proportion in this animal to be only as 24 to 36.

† Mr. Brande denies that iron exists more in the red particles of the blood than in the other principles. according to his experiments, it exists but in a very inconsiderable quantity in any of them; but he has traced it in the chyle, in the serum, and in the fibrine, or washed crassament. Phil. Trans. 1812, p. 112 Vauquelin has traced it as a constituent in egg-shells and oyster-shells. Thomson's Annals of Philos No. 1, p. 66. But Berzelius has proved Brande to be mistaken, and that iron exists largely in the blood, and is the cause of the red colour. See his Anim. Chemistry.

carbonic acid gas, by the matter of light, which he supposes to be introduced into the system in the act of respiration, instead of the matter of caloric; in consequence of which it immediately becomes a pigment. But the difficulties which attend this theory are almost, if not altogether, as numerous as those which attend the theory of combustion, and it is unnecessary to pursue the subject any farther.

In the Philosophical Transactions, and in several of the best established foreign Memoirs, we meet with a few very curious instances of spontaneous inflammation, or active combustion, having occurred in the human body. The accident has usually been detected by the penetrating smell of burning and sooty films, which have diffused themselves to a considerable distance; and the sufferers have in every instance been discovered dead, with the body more or less completely burnt up, and containing in the burnt parts nothing more than an oily, sooty, extremely fetid, and crumbly matter. In one or two instances there has appeared, when the light was totally excluded, a faint lambent flame bickering over the limbs; but the general combustion was so feeble, that the chairs and other furniture of the room within the reach of the burning body have in no instance been found more than scorched, and in most instances altogether uninjured.

It is by no means easy to explain these extraordinary facts; but they have been too frequent, and are too well authenticated in different countries, to justify our disbelief. In every instance but one the subjects have been females, somewhat advanced in life, and apparently much addicted to spirituous liquors. I shall hence only observe, in few words, that the animal body in itself consists of a variety of combustible materials; and that the process of respiration (though not completely established to be such) has a very near alliance to that of combustion itself: that the usual heat of the blood, taking that of man as our standard, is 98° of Fahrenheit, and under an inflammatory temperament may be 103° or 104°; and hence, though by no means sufficiently exalted for open or manifest combustion, may be more than sufficiently so for a slow or smothered combustion; since the combustion of a dung-hill seldom exceeds 81°, and is not often found higher in fermenting haystacks, when they first burst forth into flame. The use of ardent spirits may possibly, in the cases before us, have predisposed the system to so extraordinary an accident; though we all know that this is not a common result of such a habit, mischievous as it is in other respects. The lambent flame emitted from the body is probably phosphorescent, and hence little likely to set fire to the surrounding furniture. It is not certain whether this flame originates spontaneously, or is only spontaneously continued, after having been produced by a lighted substance coming too nearly in contact with a body thus surcharged with inflammable materials.

Such, then, are the circulatory and respiratory systems in the most perfect animals; as mammals, birds, and amphibials. It should be observed, however, that in birds the hollow bones themselves, and a variety of air-cells that are connected with them, constitute, as we have already had occasion to notice, a part of the general respiratory organ, and endow them with that levity of form which so peculiarly characterizes them, and which is so skilfully adapted to their intention. It should be remarked, also, that in most amphibious animals, and especially in the turtle, whose interior structure is the most perfect of the entire class, the two ventricles, or larger cavities of the heart, communicate something after the manner in which they do in the human fœtus. The lungs of this class are for the most part unusually large; and they have a power of extracting oxygen from water as well as from air; whence their capability of existing in both elements. The oxygen, however, obtained from the water is not by a decomposition of the water into its elementary parts, but only by a separation of such air as is loosely combined with it; for if water be deprived of air or oxygen, the animal soon expires. We have already observed that some amphibials appear to possess only a single heart, and even that of a very simple structure.

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In fishes the heart is single, or consists only of two compartments instead of four, and hence the circulation is single also. The gills in this class answer the intention of lungs, and the blood is sent to them for this purpose from the heart, in order to be deprived of its excess of carbon, and supplied with its deficiency of oxygen. It is not returned to the heart, as in the case of the superior animals, but is immedatiely distributed over the body by an aorta or large artery issuing from the organ of the gills. The oxygen in these animals is separated from the water instead of from the air; and for this purpose the water usually passes through the mouth before it reaches the gills: yet in the ray-tribe there is a conducting aperture on each side of the head, through which the water travels instead of through the mouth. In the lamprey it is received by seven apertures opening on each side of the head into bags, which perform the office of gills, and passes out by the same orifices, and not, as has been supposed, by a different opening said to constitute its

nostril.

In the common leech there are sixteen of these orifices on each side of the belly, which answer the same purpose. In the sea-mouse (aphrodita aculeata) "the water passes through the lateral openings between the feet into the cavity under the muscles of the back."

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The siren possesses a singular construction, and exhibits both gills and lungs; thus uniting the class of fishes with that of amphibials. Linnæus did not know how to arrange this curious animal, and shortly before his death formed a new order of amphibials, which he called MEANTES, for the purpose of receiving it. It ranks usually in the class of fishes.

The only air-vessels of the winged insects have a resmblance to the apertures of the lamprey, and are called stigmata. In most instances these are placed on each side of the body; and each is regarded as a distinct trachea, conducting the air, as M. Cuvier elegantly expresses it, in search of the blood, as the blood has no means of travelling in search of the air. They are of various shapes and number, and are sometimes round, sometimes oval, but more generally elongated like a button-hole. In the grasshopper they are twenty-four, disposed in four distinct rows.

The membranous tube that runs along the back of insects is called by Cuvier the dorsal vessel. It discovers an alternate dilatation and contraction: and is supposed by many naturalists to be a heart, or to answer the purpose of a heart. Cuvier regards it as a mere vestige of a heart, without contractions from its own exertion, and without ramifications of any kind: the contractions being chiefly produced by the action of the muscles running along the back and sides, as also by the nerves and tracheæ, or stigmata. Scorpions and spiders have a proper heart; and as the term insects is now confined by M. Cuvier and M. Marcel de Serres to those that have only this dorsal vessel, or imperfect heart, the two former genera are struck out of the list of insects as given by Linnæus.

This organ differs very considerably in its structure and degree of simplicity in moluscous animals. The heart of the teredo has two auricles and two ventricles; that of the oyster one auricle and one ventricle. In the muscle the heart is not, strictly speaking, divided into an auricle and ventricle, but rather consists of an oval bag, through the middle of which the lower portion of the intestine passes. Two veins from the gills open into the heart, one on each side, which may be considered as the auricles.

In several of the crustaceous insects of Linnæus, as, for example, the monoculus and craw-fish, the stigmata converge into a cluster, so as to form gills; which in some species are found seated in the claws, and in other species under the tail. These have for the most part a small single heart, and

Sir E. Home, Phil. Trans. 1815, p. 260.

↑ Home's Life of Hunter, prefixed to Hunter's Treatise on the Blood, Inflammation, &c. p. xli. En un mot, le sang ne pouvant aller chercher l'air, c'est l'air qui va chercher le sang. Leçons d'Anat. Comp. i. 23, Sect. 2, Art. 5.

See M. Marcel de Serres' Statement, Tilloch's Journal, vol. xliv. p. 148; and especially Thomson's Annals of Phil. No xxiii. p. 347, 348. 350. 354.

consequently a single circulation, the course of which, however, is directly the reverse of that pursued in fishes; for the heart in the present instance propels the blood through the body, and the gills receive it, and propel it to the heart. This is also the case in the snail, slug, and many other softbodied worms, which possess a gill in the neck, consisting of a single aperture, which it can open and shut at pleasure. Yet with a singular kind of apparent sportiveness, the cuttle-fish is possessed of three distinct hearts, which is one more than is allotted to mankind, in whom this organ is only double.

In zoophytes we are in great ignorance both as to their sanguineous and respiratory functions. That they stand in need of oxygen, and even of nitrogen, has been sufficiently determined by Sir H. Davy; as it has also that they absorb their oxygen and nitrogen, as fishes do, from the water which holds these gases in solution. Their nutrition appears to be effected by an immediate derivation of the nutritive fluid from their interior cavity into the gelatinous substance of their body.*

Hence then the respiratory organs of the animal kingdom may be divided into three classes; lungs, gills, and holes or stigmata: each of the three classes exhibits a great variety in its form, but the office in which they are employed is the same. Animals of every kind must be supplied with air, or rather with oxygen, however they may differ in other respects in tenacity of life; for a vacuum, or a medium deprived of oxygen, kills them equally. Snails and slugs corked up in small bottles have been found to live till they had exhausted the air of every particle of oxygen, and to die immediately afterward: and frogs and land-turtles, which are well known to survive the loss of the spinal marrow for months, and that of the head or heart for several days, die almost instantly on exposure to a vacuum.†

Connected with this general subject, there is still an important question to be resolved, and which has greatly occupied the attention of physiologists for the last fifty years.

The

Mediately or immediately, almost all animal nutriment, and, consequently, almost all animal organization, is derived from a vegetable source. blade of grass becomes a muscular fibre, and the root of a yam or a potato a human brain. What, then, is that wonderful process which assimilates substances in themselves so unlike; that converts the vegetable into an animal form, and endows it with animal powers?

Now to be able to reply succinctly to this question, it is necessary first of all to inquire into the chief feature in which animal and vegetable substances agree, and the chief feature in which they differ.

Animals and vegetables, then, agree in their equal necessity of extracting a certain sweet and saccharine fluid, as the basis of their support, from whatever substances may for this purpose be applied to their respective organs of digestion. Animal chyle and vegetable sap make a very close approach. to each other in their constituent principles as well as in their external appearance. In this respect plants and animals agree. They disagree, inasmuch as animal substances possess a very large proportion of azote, with a small comparative proportion of carbon; while vegetable substances, on the contrary, possess a very large proportion of carbon, with a small comparative proportion of azote. And it is hence obvious, that vegetable matter can only be assimilated to animal by parting with its excess of carbon, and filling up its deficiency of azote.

Vegetable substances, then, part first of all with a considerable portion of their excess of carbon in the stomach and intestinal canal, during the process of digestion; a certain quantity of the carbon detaching a certain quantity of the oxygen existing in these organs, as an elementary part of the air or water they contain, in consequence of its closer affinity to oxygen, and producing carbonic acid gas; a fact which has been clearly ascertained by a variety of experiments by M. Jurine of Geneva. A surplus of carbon, however, still enters the animal system through the medium of the lacteals, and continues

• Blumenbach, ◊ 167.

† See Encyclop. Brit. art. Physiol. p. 679.

to circulate with the chyle, or the blood, till it reaches the lungs. Here again a certain portion of carbon is perpetually parted with upon every expiration, in the form of carbonic vapour, according to Mr. Ellis, but according to Sir H. Davy and others, in that of carbonic gas, in consequence of its union with a part of the oxygen introduced into the lungs with every returning inspiration; while the excess that yet remains is carried off by the skin, in consequence of its contact with atmospheric air: a fact put beyond all doubt by the experiments and observations of M. Jurine, although on a superficial view, opposed by a few experiments of Mr. Ingenhouz,† and obvious to every one, from the well-known circumstance that the purest linen, upon the purest skin, in the purest atmosphere, soon becomes discoloured.

In this way, then, and by this triple co-operation of the stomach, the lungs, and the skin, vegetable matter, in its conversion into animal, parts with the whole of its excess of carbon.

Its deficiency of azote becomes supplied in a twofold method: first, at the lungs; also, by the process of respiration, as should appear from the concurrent experiments of Dr. Priestley and Sir H. Davy, which agree in showing that a larger portion of azote is inhaled upon every inspiration than is returned by every succeeding expiration; in consequence of which the portion retained in the lungs seems to enter into the system, in the same manner as the retained oxygen, and perhaps in conjunction with it; while, in union with this economy of the lungs, the skin also absorbs a considerable quantity of azote, and thus completes the supply that is necessary for the animalization of vegetable food: evincing hereby a double consent of action in these two organs, and giving us some insight into the mode by which insects and worms, which are totally destitute of lungs, are capable of employing the skin as a substitute for lungs, by breathing through the spiracles existing in the skin for this purpose, or merely through the common pores of the skin, without any such additional mechanism. It is by this mode, also, that respiration takes place through the whole vegetable world, offering us another instance of resemblance to many parts of the animal; in consequence of which, insects, worms, and the leaves of vegetables equally perish by being smeared over with oil, or any other viscous fluid that obstructs their cutaneous orifices. But to complete the great circle of universal action, and to preserve the important balance of nature in a state of equipoise, it is necessary, also, to inquire by what means animal matter is reconverted into vegetable, so as to afford to plants the same basis of nutriment which plants have previously afforded to animals?

Now this is for the most part obtained by the process of PUTREFACTION, or a return of the constituent principles of animal matter to their original affinities, from which they have been inflected by the superior control of the vital principle, so long as it inhabited the animal frame, and coerced into other combinations and productions. Putrefaction is, therefore, to be regarded as a very important link in the great chain of universal life and harmony.

The constituent principles of animal matter we have already enumerated: they are most of them compound substances, and fall back into their respective primordia as the putrefactive process sets them at liberty. This process commences among the constituent gases; and it is only necessary to notice the respective changes that take place in this quarter, as every other change

is an induced result.

*See Sir H. Davy's Researches Chemical and Philosophical, &c.; and Mémoire sur la Chaleur, par MM. Lavoisier et De la Place. Mem. de l'Acad. De la Combustion, &c.

Essaie de Théorie sur l'Animalization et l'Assimilation des Alimens, &c. Annales de Chimie, tom. ii. See Davy's Researches Chemical and Philosophical, &c.; and Priestley's Experiments and Observations on different Kinds of Air, vol. iii.

M. Jurine is chiefly entitled to the honour of this discovery: his experiments coincide with several of Dr. Priestley's results, and have been since confirmed by other experiments of MM. Lavoisier and Fourcroy See Premier Mémoire sur la Transpiration des Animaux, par A. Seguin et Lavoisier, 1792; and compare with M. Hassenfratz's Mémoire sur la Combinaison de l'Oxygen, &c. Acad. des Scien. 1791.

It should hence appear, that putrefaction is the only positive criterion of death, or the total cessation of the principle of life. Galvanism has, indeed, been advanced as a decisive proof of the same by Behrenda and Creve; but Humboldt has sufficiently shown its insecurity as an infallible test.

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