fants. They would be eaten into the bone by vera min, were they not to duft themfelves often, in or der by this means to get rid of their troublesome lodgers. Storks and pidgeons are allo very fubject to them. It is faid that there is a bird in the Brazils, called Taputa, which confifts of nothing but fkin, and bone and vermin. The infects do not fix indifferently on all parts of the bird they adhere to. Some lodge under the fim, particularly about the neck, where the bird cannot easily get at them with his bill; others on the quills of their feathers; others on the wings &c. An attentive obferver with little trouble may easily convince himself of thefe facts.

Infects do not lefs infeft quadrupeds than birds. The Gad-fly pierces the fkin of cows, deer and hogs, and depofits its eggs; the larvæ afterwards nelle between the fkin and the flefh. Some are found in the heads of various animals, but chiefly in thofe of the deer kind. To this fome people have attributed the annual cafting of their horns. They infinuate themselves alfo into the nofes of different quadrupeds. Shepherds know but too well how fatal they are in this cafe to the fheep they attack. Some penetrate even to the inteftines, and move there as if in long galleries. Such are found in the inteftines of horfes; but befides thefe, what vaft numbers of infects attach themfelves externally to quadrupeds? Some flies chiefly infeft dogs, others horis. Different fpecies of pediculi adhere firmly to the fkins of affes, dogs, horfes, deer, fheep, &'c.

Man the most noble of animals, is a world inhabited by multitudes of infects. The famous Borelli, an author who certainly is intitled to credit, affirms that he difcovered in human blood animalcules of a figure fimilar to that of whales, fwimming in it, as

in a red fea. Other writers, equally learned and curious, mention larvæ found in the human brain, which proved fatal to fome, tho' others were happily relieved from them. Infects likewife find their way into the human ftomach, whence they are expelled by means of emetics. Our inteftines, are not more exempt from them than thofe of other animals, as I had occafion to mention above. Our whole body, fo to fpeak, is like a ftorchoufe which furnishes food to an infinite number of infects. Some lodge between the fkin and the flesh where they live at our expence. Young children who are not kept clean, are chiefly expofed to the attacks of vermin; and fometimes it has become neceffary to make incifions in order to extract them from the nofe, the eye brows, the ears, and the tongues of many perfons. There are fometimes animalcules under the fkin of the hand, which creep along and make little elevations fimilar to thofe made in the earth by a mole. The Indians often have the leg and fole of the foot attacked by long worms which cannot be extracted without the greateft precaution. If they are broken, and the leaft part remain in the limb or in the foot, the life of the perfon becomes endangered. There is alfo in the Îndies a small kind of flea called nigua (Pulex penetrans) which is likewife exceedingly troublefome. It burrows between the nail and the flesh of the toes, making them iwell to fuch a degree, that it is neceffary to make an opening in them. One would think that the hardness of the bones would fecure them from the infults of thefe animalcules; and yet some are found living and feeding there. It is needlefs to mention thofe that infeft the external parts of our bodies, they are too well known. I fhail therefore ftop for a moment to confider the wonderful difcoveries made by Leewenhoeck in the femen of anis mals.

That illuftrious obferver of nature perceived with his microfcope an infinite number of fmall animals fwimming in the fpermatic liquor. This difcovery made him conjecture that the ftrongest and most vigorous of thefe animalcules were arrefted in the matrix, where they were nourished, and grew and became at last a perfect foetus. What confirmed him the more in his opinion was, that in opening a female rabbit, immediately after its commerce with the male, he found in the matrix a vaft number of thefe living animalcules. The obfervations he made on the femen of different perfons feemed to make the thing certain. In that of a boy, there was nothing feen but little black points without motion; while in that of a young man fully grown, there were myriadst moving about with the greatest activity. In that of old men fome indeed were found, but they were without ftrength or vigour and almost dead. Lastly in people that were fterile, these animals were not difcovered, or if they were discovered, they were dead.

But he carried his obfervations further, and thought he could diflinguifh the different fexes in thefe animalcules: whence he concluded that animals conceived males or females according as the different fexes were detained in the matrix, where they were foftered, and received enlargement.

Thefe animalcules are exceedingly fmall, and Leewenhoeck fays, that a drop like a grain of fand contained many thoufands of them. He found them fmaller than thofe globules that give to blood its red colour, and he thinks that the place occupied by a grain of fand, might contain an hundred thoufand. Their bodies are round, growing fomewhat thick towards the head, and gradually diminishing towards the tail, which is five or fix times longer, and about

five and twenty times more flender than the reft of the body; it is likewife tranfparent. They bend it a little, and move themfelves like eels in water. There is a very great difference between the young of thefe animalcules, and thofe that are come to maturity. The first have the body more slender, the tail three times fhorter, and lefs pointed than the latter. In the femen of a ram, thofe animalcules fwam in a ftring one after another, as theep do in water.

Many learned men have made the fame obfervations after Leewenhoeck. In this number are Huygens, Andry, Valifnieri, Wolff and Tummig. Cartheufer fhewed thefe animalcules fome years ago at Halle in his lectures on experimental philofophy to more than fixty perfons. Hartfoeker examined, during a course of thirty years the femen of a vast number of quadrupeds and birds. He compares the fpermatic animalcules of the first to the tadpoles frequent in ftagnant waters, which have not yet got feet; thofe of birds refemble fmall worms or a very slender thread. These observations made him fuppofe that there were only two kinds of fpermatic animalcules to wit, thofe of quadrupeds, and thofe of birds. He did not deny that there might be diverfities according to the different fpecies, efpecially between thofe of man and quadrupeds; but he faid that thefe were not difcernible on account of their minutenefs and the velocity of their motions.

The defenders of this doctrine difagree when they come to explain how thefe animalcules contribute to the generation of the particular fpecies of animal which has produced them. Some with Leewenhoeck believe that in the intercourfe of viviparous animals, one or more of thefe animalcules attach themfelves, to the matrix, that others ferve for their food, and that

L 2

at laft they become a perfect foetus. They add that the ova in the ovarium, only produce the fecretion of certain fluids. In oviparous animals the egg anfwers the end of the matrix, and to it the animalcule attaches itfelf. It penetrates into the middle of the yolk where it gradually grows to its perfection. Other authors diffent from this fyllem, and maintain that, in copulation, one or more of these animalcules get up into the ovarium by the Fallopian tubes, and there penetrate into an egg, at that time in a proper ftate to receive them, by means of an aperture furnithed with a valve which prevents their retreat.

in this

egg it is nourished and grows. Laftly, fome authors affirm that these animalcules have not yet the figure of a foetus, and that they receive it by a transformation fimilar to that of a caterpillar changing into a butterfly.

I fhall not venture to decide on these various opinions, or to determine whether the animalcules are neceffary to procure conception, whether they ferve only to caufe a voluptuous titilation, or if they are deftined to any other ufe; ftill lefs will I fupport the opinion I have detailed. It appears to me too fingu lar, and liable to too many difficulties, as various authors have fhewn. It is certain, however, that thefe permatic animalcules are worms of a particular kind, destined by the Creator to ferve a particular purpofe; but inan has not yet difcovered that deftination, fo great is the imperfection of human know ledge.

I had almoft forgot to mention that infects are found in the dry remains of plants and animáls, as well as in works of art. There are fome dry legumes which have the fhell as hard as that of a nut but this hardnefs does not fecure them from the piercing teeth of fome infe&s which reduce them to powder.