Natural Pumps.
257
Chap. 2.]
their bodies : oysters and some other shell fish move in this manner. My-riads of marine animals also ascend and descend in their native element bymeans of forcing pumps : when about to dive, they admit water mto cer-tain receptaoles, and in such quantities as to render their bodies speci-fically heavier than the fluid they float in; and when they wish to ascend,they pump out the water which carried them down.
That expert gunner, the jaculator fish, shoots his prey with pellets orglobules of water as from a piston pump. When an insect hovers near orrests on some aquatic plant within five or six feet of him, he shoots fromhis tubulär snout a drop of water, and with so “ sure an aim as generallyto lay it dead.” The habit of ejecting saliva, which some persons ac-quire, is by making a pump of the mouth and a piston of the tongue.Other animals practice the sams; thus the llama of Chili and Peru , whenirritated, “ejects its saliva to a considerable distance”—Frezier says tenpaces, or thirty feet. The spurting snake of Southern Africa , it is said,ejects its poison into the eyes of those who attack it with unerring aim.The tongue of the lamprey moves backwards and forwards like a piston,and prodüces that suct.ion which distinguishes this animal and others of thesame family. The sting of some inseots, that of the bee, for example, isa very complex apparatus, consisting of a lancet with its sheath, to pene-trate the bodies of their enemies; first acting as a trocar and canular, andthen as a pümp to 1 force poison into the wound—“ an awl to bore a hole,[says Paley,] and a syri-nge to inject the fluid.”
It perhaps may be supp'osed from the form of common pumps, thatthere is li'ttle resemblance between them and these natural machines, butit should be' remembered that this form is purely arbitrary, (they are, aswe have already seen, sometimes made of flexible ma.terials, and alter-nately dilated and collapsed like the chests of animals.) The generalcustom of making them of hollow cylinders and of inflexible materials,arose from experience having proved that when thus made, they are moredurable and less liable to derangement than any others that have yet beendevised.
The circulation of the blood in man and other animals is effected byapparatus strikingly analogous to sucking and forcing bellows pumps. Theheart is one of these—the arteries are its forcing, the veins its suctionpipes, and both pump and pipes are furnished with the most perfectyalves. By contraction, this wonderful machine forces the blood throughthe former to the uttermost parts of the System ; and by distension, drawsit back through the' latter. a They Vary in dimensions as in construction.Some are adapted to' the bodies of animals so minüte as to be impercep-tible to unaided vision, and from these to others of every size up to thehuge leviathan of the deep. The aorta of the whale, says Paley, “ islarger in the bore than the main pipe of the water-works at Londonbridge; and the' water röaring in its passage through that pipe, is inferiorin impetus and velocity to the blood rushing from the whale’s heart.”
Every human beihg may be cbnsidered as, nay is, a living pump. Hisbody is wholly made up of it, of the tubes belonging to it, and the liquidmoved by it—with such additions as are required to communicate the ne-cessary motion and protect it from ihjury. Health, life itself, every thing,depends upon keeping it in Order. If one of its forcing pipes, (an artery,)be severed, we bleed to deäth ; are any of its sucking tubes (the veins)