parative quantities consumed by the rabbit and the horse; the former soon consumes a quantity equal to its own bulk, but a quantity equal to the bulk of the horse would not be consumed by him in several weeks. An animal that is not kept in relation with the laws of the material world, by the combined action of its arterial and nervous system, may remain months without food, without undergoing a chemical decomposition, as may be observed in the dormouse, and other hybernating animals; and, for a much longer period, as has been known of flies, which have remained torpid for years. On the contrary, animals who are excited to a preternatural vigilance, require unusual quantities of food. The required supply of food then does not correspond with the size of the animal, but is increased in the smaller, and decreased in the larger sensibility has also been shown to be necessarily increased in the smaller, and decreased in the larger, animals: from these circumstances, and the facts of torpid animals living without food, while those who are preternaturally excited, require unusual quantities, I am led to conclude, that the required quantity of food corresponds very much (although as I shall hereafter show, not altogether) with the required degree of sensibility, and hence, that

the ultimate use of the assimilative organs and food-taking is, the supply of electric fluid, upon the agency of which I have assumed sensibility to be dependent.

This view of the ultimate uses of the assimilative organs will be further borne out in a more extended consideration of animal existence, for which we shall hereafter be better prepared, by an advanced examination of the circumstances connected with life in the next part of our inquiry, as well as by a consideration of the nature of some diseases to be spoken of in a later part of this paper.

CHAPTER V.

The Lungs-bring the blood into contact with the air -supposed object of this-questioned-and disproved -Animal heat-no fixed degree essential to lifethe degree of heat an adventitious circumstancesource of heat and use of the Lungs-argument in support-on media influencing the degree of heatFishes-Amphibia-Insects-Conclusion.

SITUATED in, and nearly filling, the chest, (in man) are some fleshy sponge-like bodies, very permeable to air and exceedingly vascular, called Lungs. The evident design of these bodies, apparent both from their structure and function, is to bring into contact with the surrounding medium a large surface of the circulated blood. Of the exact chemical combinations and results thus effected, there is but little agreement among experimenters, scarcely any two inquirers having come to the same conclusion. These organs, however, are of such considerable importance in the animal economy, and, unfortunately in this country, so frequently the seat

of destructive disease, that they claim on both accounts a deep interest and a cautious consideration. Without, therefore, entering into a tedious discussion of the chemical affinities there exercised, or considering their secondary uses in the exercise of the voice, I shall proceed to investigate and treat of their primary use and importance as subservient to life. Their use has long been considered in connection with animal heat, and the most prevailing and commonly-received opinion is that proposed by the ingenious Dr. Crawford, founded upon Dr. Black's Theory of Latent Heat. He assumes, that arterial and venous blood have different capacities for caloric, and that the capacity is least in venous blood, and hence, that heat becomes sensible in that state; then, as a quantity of heat is continually given out from the body, the blood passes through the lungs in order to receive from the air materials for a further combustion, and the principle, thought to be received for that purpose, is oxygen. This theory, notwithstanding the supposed analogy between breathing and combustion, which has been so much dwelt upon by its supporters, is opposed by so many facts, requires so many unsupported assumptions, and is so at variance with nearly all the phenomena of disease, that

it cannot have been received from any conviction it carries with it, nor from any tendency which it has to clear up the mysteries of life. For, although Dr. Black has shown, and it may be clearly comprehended, that bodies have different capacities for caloric, yet it has never been supposed that their capacities are changed by mere change of situation; and it requires some stretch of the imagination to suppose that blood in an artery, and the same blood in a vein has different capacities for heat. But its fallacy cannot be doubted, when it is reflected, that heat is given out in an incubated egg, in which case there is no constant supply of oxygen; and that, in cases where persons die from an insufficient supply of oxygen, as in those who breathe the gases from lime-kilns and charcoal, the heat of the body becomes much increased previous to death; and, if oxygen be here timely supplied, the heat diminishes and the patient recovers. In extensive inflammation, a much greater quantum of heat is evolved than in health, although the action of the lungs be not increased. Another, the most important objection to this theory is, that in pulmonary consumption, where the lungs become much wasted, the heat of the body, instead of being diminished, as it must have been if such theory had been true,