Domestic Encyclopædia (1802)/Amphibious Animals
AMPHIBIOUS ANIMALS are so called, on account of their living partly on land, and partly in water.
We cannot, consistently with our plan, enter into a disquisition respecting their nature and functions; and shall therefore content ourselves with observing, that in their structure, they are principally distinguished from land-animals, by having red cold blood, and instead of lungs, either gills or branchiæ, as is generally observed in snakes, eels, and fish, which chiefly inhabit the water. Sometimes, however, they have the oval hole open between the right and left auricles of the heart; and, in many, the arterial canal is also free. This is a distinguishing character of the phocæ, or such animals as enjoy their chief functions on land, for instance, otters, beavers, frogs, crocodiles, some kind of rats, birds, &c. While these remain under water, where they may safely continue for several hours, their respiration is interrupted; and the blood, not finding a free passage through the pulmonary artery, rushes through the hole from the right to the left auricle, and partly through the arterial canal; having but a short course to the aorta, the largest of all the blood vessels, and thence circulating to every part of the body. But, on rising to come ashore, the blood makes its way again through the lungs, as soon as the animal begins to respire.
As in all land animals a large portion of the mass of blood continually circulates through the lungs, which would be stopped, if the free access of air were excluded; so we find in fish a great number of blood-vessels passing through the gills, which must be perpetually wet, lest the blood should, in like manner, be checked, and consequently stagnate in its progress. Hence, when the latter are removed from their natural element, the branchiæ very soon grow crisp and dry, the vessels become corrugated, and the blood finds no outlet: likewise, when land-animals are immersed under water, or in any other manner deprived of respiration, the circulation ceases, and the animal inevitably dies.
Inquisitive physiologists have advanced, that man may, by art, be rendered amphibious, and enabled to live under water, as well as the beaver, or turtle; because the fœtus in utero lives without air, and the circulation is continued by means of the oval hole: if, therefore, this important opening could be preserved after the birth of the child, the same useful faculty might still remain.
This proposition is plausible; and we do not hesitate to declare, that in a maritime country, such attempts ought by all suitable means to be encouraged: for the advantages resulting from a successful application of the theory, would indeed be incalculable. In its support, and as an instance of the wonderful power we possess over the organs of respiration, it may be urged, that expert divers feel no inconvenience from remaining for several minutes under water, at a considerable depth; that individuals affected with asthma (among whom the writer of this article is a living evidence) have by mere force of habit obtained effectual and permanent relief in that distressing complaint, by accustoming themselves from the commencement of it, to respire principally through the nostrils, whether in a waking or sleeping state; and lastly, that none of the interior organs possess a flexibility and power of expansion (unattended with loco-motion) equal to those of respiration.
After this short digression, we shall proceed to state the means by which that desirable faculty of respiring under water, may be acquired by the human subject.
It should previously be remarked, that the lungs of the embryo are compressed during its confinement, so that the pulmonary blood-vessels are impervious, and consequently the circulation must take place through the oval hole, and the arterial canal before-mentioned: hence the amphibious animal and the fœtus in utero are so far analogous in their nature; and though this hole generally closes at an early period of infancy, yet there are instances, well attested by anatomists, where it has been occasionally found not quite closed in human subjects, who have died at an advanced age. There is, however, one material difference between them: the fœtus never having respired, is sufficiently nourished by the maternal blood circulating through its whole body, which progressively grows, till its birth, without feeling the want of respiration during the whole period of pregnancy; on the contrary, terraqueous animals having respired from the moment of their birth, cannot support life for any length of time without it; because both the hole and canal above alluded to would be closed, or at least constricted in them, as is the case in land animals, if they did not instinctively, soon after the birth of the cub, instruct it in the exercise of that vital function. This is effected, by frequently carrying it into the water—a practice by which these passages are kept open during life, and the creatures enabled to procure that kind of food which is designed for them by the providential care of Nature.
Thus we may easily conceive that, in infants, the oval hole, by proper expedients and persevering exertions, might, without much difficulty, be preserved in an open state; for instance, by gradually accustoming young children, soon after their birth, to suspend their breath once, or oftener in a day, increasing the duration of the experiment with every attempt, so that the blood may at length be directed to circulate through its original passage, which, by several trials, cautiously repeated, would no doubt remain sufficiently lubricated, and never again be closed in the manner we generally find it in the deceased body.
That these are rational, and, we may venture to add, well founded conjectures, few will dispute; especially if it be considered that ordinary divers, without having been trained to this practice from early infancy, are capable of retaining their breath, and continuing much longer under water, than persons in whom that primitive organ of respiration, having never been exercised, has become unfit to act as an useful substitute for the lungs, while immersed under water.—Nay, there are well authenticated instances of persons who were in the full possession of the uncommon faculty here described: of others, we shall relate only that of a Sicilian, named the Fish-Colas, who possessed it in so eminent a degree, "that he lived rather after the manner of a fish than a man," in consequence of having from his youth, and by an assiduous practice, successfully acquired the habit of living in water, and thus effected a complete change of his physical nature.
We shall conclude tliis interesting subject with a short account of the alimentary uses, and properties, of amphibious animals.
In some countries, especially in old France and Italy, the legs of frogs were esteemed a delicate dish; but, in Britain, we regale our friends with the more delicious turtle. Yet these testaceous creatures, as well as animals of this class in general, and the West Indian guana in particular, contain an unusual proportion of fat; and ought, therefore, to be eaten not only with great moderation, but also with a considerable addition of salt, and acid: the former, for the purpose of neutralizing them into a saponaceous mass, which is most easily assimilated to our fluids; the latter, with a view to counteract their putrescent tendency, especially in warm seasons—both, in order to facilitate their digestion in the human stomach.