sis and hyperbola. Mr. D'Alembert has purfued the same aubject and carried it farther, in Mem. de L'Acad. de Berlin. Tom. 2. p. 200. seqq.
FLUIDS (Cycl.)—Animalcules observed in fluids are of divers kinds; some are flat, others eel like, but the greater part of an oval figure. Leewenhoeck gives a descriptionof a very unusual shaped creature, fixed in a little scabbard or sheath; which was fastned to some of the small green weeds found in ditches full of water. Phil. Trans. N°. 337. p. 160.
Waters of all kinds that have stood a while exposed to the air, till they have grown a little putrid, or where putrefaction has been promoted by the admixture of other matters, abound in variety of animalcules, having each their peculiar characters, sizes, figures, economy, and method of life, not to say uses. In a small drop of the discoloured surface of rain water, which had flood two months in a window, Dr. Harris observed four forts of animalcules: the clear part of the drop presented two kinds, both very small; the first of the figure of ants eggs: these were in a continual brisk motion. The second more oblong, three times as long as broad, were exceedingly numerous, but their motion flow.
In the thick part of the drop there were also two sorts of animalcules. The first of the eel kind, resembling those in vinegar, but much smaller, and with their extremes more sharp. These would wriggle out into the clear part, and then suddenly betake themselves back again, and hide in the thick and muddy part of the drop, much like common eels in the water. The second sort resembled a large maggot, which would contrail themselves into a spherical figure, and then stretch out again. The end of the tail appeared with a forceps, like that of an ear-wig. They might be plainly perceived to open and shut their mouths, from whence air bubbles were frequently discharged. The number of these was not above four or five. The fame four kinds of animalcules he also found in many other drops of the fame corrupted water.
Animalcules in Fluids, are generally found at the top. In the lower parts of the water, Mr. Harris assures us he could never find any, unless when the liquor had been disturbed, and the surface shaken down, and mingled with the lower parts. Mr. Harris examined some rain water that had flood uncovered a pretty while, but had not contracted any thick or discoloured scum.
And here where the water was clear, he could not find any animals at all; but a little thin white scum, that like grease began to appear in its surface, he found to be a congeries of exceeding small animals of different shapes and sizes, much like those produced by sleeping barley in water.
Viewing a small drop of the green surface of slime puddle water, he found it altogether composed of animalcules of several shapes and magnitudes; the most remarkable, were those which gave the water that green colour, and were oval creatures, whose middle parts were of a grass green, but each end clear and transparent. They would contract and dilate themselves, tumble over and over many times together, and then shoot away like fishes. Phil. Trans. N°. 220, p. 255.
Mr. Harris looked on the surface of some mineral chalybeate water, which had flood in a vial unstopt for about three weeks. In it he saw two kinds of animals. One exceeding small, and the other very large, which latter fort had on the tail, something that look'd like fins. There were but very few of either fort. Phil. Trans. N . 220. p. 257. seqq.
Animalcules in Fluids are easily destroyed by only separating them a while from their element. Naturalists have even found shorter ways. A needle point dipped in spirit of vitriol and then immersed into a drop of pepper water, readily kills all the animalcules, which tho' before frisking about with great liveliness and activity, no sooner come within the influence of the acid particles, then they spread themselves and tumble down to all appearance dead. The like may be done by a solution of salt, only with this difference; that by the application of this latter, they seem to grow vertiginous, turning round and round, till they fall down. Tincture of salt of tartar used in the same manner kills them still more readily; yet not so, but there will be apparent marks of their being sick first and convulsed. Inks destroy them as fast as spirit of vitriol, and human blood by virtue of the fast contained in it, produces the same effect. Urine, sack, and sugar, do all destroy them, tho' not so fast; besides, that there is some diversity in their figures and appearances, as they receive their deaths from this poison, or that[1]; the point of a pin dipped in spittle presently killed all the kinds of animalcules in puddle water, as Mr. Harris supposes it will other animalcules of this kind[2]
We find in the waters of our ditches many species of small animalcules, both of the crustaceous and testaceous kinds. The legs of the creatures are short, they resemble those of crabs and lobsters, but are of a much more curious structure; they are less than a small flea, but they seem all breeders, carrying spawn at their tails, or in two small bags, one hanging from each side. These bags are often seen broken, and the spawn is then found to consist of globules very large in proportion to the size of the creature. There is another fort beside these as beautiful but much smaller than they; this in shape more resembles the shrimp, and carries its spawn as the shrimp does. These kinds both seem to have only one eye and that placed exactly in the middle of their forehead, without the least trace of a dividing line; and they are often so transparent that the motion of their bowels, and pulsation of their heart may be seen. Baker's Microscope, p. 93.
All who are acquainted with the microscope, know very well, that in water, in which the best glasses can discover no animated particle of matter, after a few grains of pepper, or a small fragment of a plant of almost any kind has been some time in it; animals full of life and motion are produced, and those so numerous as to equal the fluid itself in quantity.
When we see a numerous brood of young fishes in a pond, we make no doubt of their having owed their origin to the spawn that is, the eggs of their parents of the same species. What are we then to think of these? if we will consider the progress of nature in the insect tribes in general, and especially in such of them as are most of all analogous to these, we shall find it less difficult to give an account of their origin, than might have been imagined.
A small quantity of water taken from any ditch in the summer months, is found to be full of little worms, seeming in nothing so much as size, to differ from these microscopic animalcules, Nay water without these exposed in open vessels in the summer months will be always found after a few days to abound with multitudes of them, visible to the naked eye, and full of life and motion.
These we know by their future changes are the fly worms of the different species of gnats, tipulæ, and multitudes of the other fly-species; and we can easily determine, that they have owed their origin only to the eggs of the parent fly there deposited. Nay a closer observation will at any time give ocular proof of this; as the flies may be seen laying their eggs there, and those eggs; may be followed in all their changes to the fly again. Why then are we to doubt but that the air abounds with other flies and animalcules, as minute as the worms in these fluids? and that these last are only the fly-worms of the former, which after a proper time spent in that state will suffer changes like those of the larger kinds, and become flies like those to whose eggs they owed their origin? Vid. Reaumur, Hist. Insect. vol. 4. p. 431.
The differently medicated liquors made by the infusions of different plants, afford a proper matter for the worms of different species of these small flies; and there is no reason to doubt but that among these some are viviparous, others oviparous, and to this may be in a great measure owing the different time taken up for the production of the insects in different fluids, Those which are a proper matter for the worms of the viviparous fly, may be soonest found full of them, as probably the liquor is no sooner in a state to afford them a proper nourishment, than their parents place them there: whereas those produced from the eggs of the little oviparous flies must after the liquor is in a proper state, and they are deposited in it in form of eggs, have a proper time to be hatched before they can appear alive.
It is easy to prove that the animals we find in these vegetable infusions were brought thither from elsewhere. It is not less easy to prove that they could not be in the matter infused, any more than in the Fluid it is infused in.
Notwithstanding the fabulous accounts of salamanders, it is now well known, that no animal large or small, can bear the force of fire for any considerable time; and by parity of reason we are not to believe, that any insect or embryo insect, in any state can bear the heat of boiling water for many minutes. To proceed to inquiries on this foundation, if several tubes filled with water with a small quantity of vegetable matter, such as pepper, oak bark, truffles, &c. in which after a time, insects will be discovered by the microscope; and other like tubes be filled with simple water boiled, with water and pepper, boiled together, and with water with the two other ingredients, all separately boiled in it; when all these liquors come to a proper time for the observation of the microscope, all, as well those which have been boiled, as those which have not, will be found equally to abound with insects, and those of the same kind in the infusions of the same kind, whether boiled or not boiled.
Those in the infusions which had sustained a heat capable of destroying animal life, must therefore not have subsisted either in the water, or in the matters put into it, but must have been brought thither, after the boiling, and it seems by no way so probably, as by means of some little winged inhabitants of the airdepositing their eggs or worms in those Fluids.
It is a natural question on this to ask, why it is, that while we see myriads of the progeny of these winged insects, in water we never see themselves. The answer is equally easy, viz., because we can always place a drop of this water immediately before the focus of the microscope, and keep it there while we at leisure examine its contents; but that is not the case with regard to the air inhabited by the parent flies of these our worms, which is of immense extent in proportion to the water properto
