difcover if animals covered with a hard fhell, fuch as crabs, are infefted with any fort of vermin; this is not impoffible, fince fome writers affirm that they, have found fuch on fhell fifh. Oyfters are faid to have infects with many feet in them, and we fee evidently that the hells of fea fnails and muscles have been eaten by worms. Fishes though living conftantly in water, and having their bodies covered with fcales, are not exempt from the infults of infects; thefe attack the most monftrous whale, as well as the smallest fish. Some harbour under the fcales, as under a roof; others attach themfelves near the very eyes, and adhere fo strongly, that notwithstanding the rapi dity of the fith, it cannot fhake them off. Others infinuate themselves under the ears of whales, and are there nourished; others pierce the flesh, and penetrate fo deeply, that they cannot be feen or expelled. Some glide into the inteftines which they pervade in all directions; or fettle in the stomach. Many authors have obferved that infects harbour in the feathers of birds; not however always in equal numbers; for in autumn, there are fewer of them than at any other feason. The caufe of this may be, that they are then fatter, and that they have imparted a good number of these attendants to the young they have hatched. Those who have the care of poultry yards, know that pullets and geefe, are attacked by vermin, and this is perhaps the reason why hawks are fo tormented with them. The birds they seize, communicate these vermin to them which they never can afterwards rid themfelves of. If we may believe the teftimony of authors, cranes have alfo a great number of infects adhering to them. The fame is to be faid of Peacocks, and Turkies; but few birds are more cruelly infefted with them than phea fants. fants. They would be eaten into the bone by ver min, were they not to dust themfelves often, in or der by this means to get rid of their troublefome lodgers. Storks and pidgeons are alfo very fubject to them. It is faid that there is a bird in the Brazils, called Taputa, which confifts of nothing but skin, and bone and vermin. Thefe infects do not fix indifferently on all parts of the bird they adhere to. Some lodge under the fkin, particularly about the neck, where the bird cannot eafily 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 eafily convince himself of these 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 neftle 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 noses 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 intestines, and move there as if in long galleries. Such are found in the inteftines of horfes; but befides thefe, what vast numbers of infects attach themfelves externally to quadrupeds? Some flies chiefly infeft dogs, others horfes. 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 discovered 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 stomach, 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 ftorehoufe 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 those 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 Indies a small kind of flea called nigua (Pulex penetrans) which is likewife exceedingly troublesome. It burrows between the nail and the flesh of the toes, making them fwell 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 fome 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 fhall therefore ftop for a moment to confider the wonderful difcoveries made by Leewenhoeck in the femen of animals. L That That illuftrious obferver of nature perceived with his microscope an infinite number of fmall animals. fwimming in the fpermatic liquor. This discovery made him conjecture that the strongest and most vigorous of thefe animalcules were arrefted in the matrix, where they were nourished, and grew and became at last a perfect fetus. 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 these living animalcules. The obfervations he made on the fe'men of different perfons feemed to make the thing certain. In that of a boy, there was nothing seen but little black points without motion; while in that of a young man fully grown, there were myriads moving about with the greatest activity. In that of old men fome indeed were found, but they were without strength or vigour and almost dead. Lastly in people that were fterile, these animals were not difcovered, or if they were difcovered, they were dead. But he carried his obfervations further, and. thought he could diftinguifh 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 thousand. 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 rest of the body; it is likewife transparent. They bend it a Little, and move themselves like eels in water. There is a very great difference between the young of these 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, those animalcules swam in a string one after another, as sheep do in water. 1 Many learned men have made the fame obfervations after Leewenhoeck. In this number are Huygens, Andry, Valifnieri, Wolff and Tummig. Cartheufer fhewed these 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, especially between those of man and quadrupeds; but he faid that these 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 species of animal which has produced them. Some with Leewenhoeck believe that in the intercourfe of viviparous animals, one or more of these animalcules attach themselves, to the matrix, that others ferve for their food, and L 2 that |