almost as difficult to comprehend as those of the fimpleft degrees of animation. Thus the elaftic gum, or caoutchouc, and fome foffile bitumens, when drawn out to a great length, contract themfelves by their elasticity, like an animal fibre by ftimulus. The laws of action of thefe, and all other elastic bodies, are not yet understood; as the laws of the attraction of cohefion, to produce these effects, must be very different from those of general attraction, fince the farther the particles of elastic bodies are drawn from each other till they feparate, the ftronger they seem to attract; and the nearer they are preffed together, the more they seem to repel; as in bending a spring, or in extending a piece of elaftic gum; which is the reverfe to what occurs in the attractions of difunited bodies; and much wants further inveftigation. So the fpontaneous production of alcohol or of vinegar, by the vinous and acetous fermentations, as well as the production of a mucus by putrefaction which will contract when extended, feems almoft as difficult to understand as the fpontaneous production of a fibre from decompofing animal or vegetable subftances, which will contract when ftimulated, and thus conftitutes the primordium of life.

Some of the microfcopic animals are faid to remain dead for many days or weeks, when the fluid in which they existed is dried up, and quickly to recover life and motion by the fresh addition of

water and warmth. Thus the chaos redivivum of Linnæus dwells in vinegar and in bookbinders pafte; it revives by water after having been dried for years, and is both oviparous and viviparous ; Syft. Nat. Thus the vorticella or wheel animal, which is found in rain water that has ftood fome days in leaden gutters, or in hollows of lead on the tops of houses, or in the flime or fediment left by fuch water, though it difcovers no fign of life except when in the water, yet it is capable of continuing alive for many months though kept in a dry state. In this ftate it is of a globulous fhape, exceeds not the bignefs of a grain of fand, and no figns of life appear; but being put into water, in the space of half an hour a languid motion begins, the globule turns itself about, lengthens itfelf by flow degrees, affumes the form of a lively maggot, and moft commonly in a few minutes afterwards puts out its wheels, fwimming vigorously through the water as if in fearch of food; or elfe, fixing itself by the tail, works the wheels in such a manper as to bring its food to its mouth; English Encyclopedia, Art. Animalcule.

Thus fome fhell-fnails in the cabinets of the curious have been kept in a dry ftate for ten years or longer, and have revived on being moiftened with warmish water; Philof. Tranfact. So eggs and seeds, after many months torpor, are revived by warmth and moisture; hence it may be concluded,

that even the organic particles of dead animals may, when exposed to a due degree of warmth and moifture, regain fome degree of vitality, fince this is done by more complicate animal organs in the inftances above mentioned.

The hydra of Linnæus, which dwells in the rivers of Europe under acquatic plants, has been obferved by the curious of the prefent time, to revive after it has been dried, to be restored after being mutilated, to multiply by being divided, to be propagated from fmall portions, to live after being inverted; all which would be beft explained by the doctrine of fpontaneous reproduction from organic particles not yet completely decomposed.

To this fhould be added, that these microscopic animals are found in all folutions of vegetable or animal matter in water; as black pepper fteeped in water, hay fuffered to become putrid in water, and the water of dunghills, afford animalcules in astonishing numbers. See Mr. Ellis's curious account of Animalcules produced from an infufion of Potatoes and Hempfeed; Philof. Tranfact. Vol. LIX, from all which it would appear, that organic particles of dead vegetables and animals, during their ufual chemical changes into putridity or acidity, do not lose all their organization or vitality, but retain fo much of it as to unite with the parts of living animals in the procefs of nutrition, or unite and produce new complicate animals by fecretion as

in generation, or produce very fimple microscopic animals or microscopic vegetables, by their new combinations in warmth and moisture.

And finally, that these microscopic organic bodies are multiplied and enlarged by solitary reproduction without fexual intercourse till they acquire greater perfection or new properties. Lewenhoek obferved in rain-water which had flood a few days the fmallest scarcely visible microscopic animalcules, and in a few more days he observed others eight times as large; English Encyclop. Art. Animalcule.

CONCLUSION,

There is therefore no abfurdity in believing that the most fimple animals and vegetables may be produced by the congrefs of the parts of decompofing organic matter, without what can properly be termed generation, as the genus did not previously exift; which accounts for the endless varieties, as well as for the immenfe numbers of microfcopic animals,

The green vegetable matter of Dr. Priestley, which is univerfally produced in flagnant water, and the mucor, or mouldinefs, which is feen on the furface of all putrid vegetable and animal matter, have probably no parents, but a spontaneous origin from the congress of the decompofing organic particles, and afterwards propagate themselves. Some other fungi, as thole

growing in close wine-vaults, or others which arise from decaying trees, or rotten timber, may perhaps be owing to a fimilar spontaneous production, and not previously exist as perfect organic beings in the juices of the wood, as fome have fuppofed. In the fame manner it would feem that the common efculent mushroom is produced from horse dung at any time and in any place, as is the common practice of many gardeners; Kennedy on Gardening,

APPENDIX.

THE knowledge of microscopic animals is ftill in its infancy: those already known are arranged by Mr. Muller into the following claffes; but it is probable, that many more claffes, as well as innumerable individuals, may be difcovered by improvements of the microscope, as Mr. Herschell has difcovered fo many thoufand ftars, which were before invifible, by improvements of the telescope.

Mr. Muller's claffes confist of

I. Such as have no External Organs.
1. Monas: Punctiformis. A mere point.
2. Proteus: Mutabilis. Mutable.
3. Volvox: Sphæricum. Spherical.
4. Enchelis: Cylindracea. Cylindrical.
5. Vibrio Elongatum. Long.

Membranaceous.

6. Cyclidium: Ovale. Oval.

7. Paramecium: Oblongum. Oblong.