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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 dunghill seldom exceeds 81°, and is not often found higher in fermenting hay-stacks 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 characterises 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 foetus. The lungs of this class are, for the most part, unusually large; and they have a power of extracting oxygene from water as well as from air; whence their capability of existing in both

*Vol. I. Ser. 1. Lect. xI. p. 251.

elements. The oxygene, 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 oxygene, 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.

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 carbone, and supplied with its deficiency of oxygene. It is not returned to the heart, as in the case of the superior animals, but is immediately distributed over the body by an aorta or large artery issuing from the organ of the gills. The oxygene 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."*

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 resemblance 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 buttonhole. 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 exhibits 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

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.

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 molluscous 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 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.

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

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