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discover is animals covered with a hard shell, such as Crabs, are infested with any fort of vermin; this is not impossible, since some writers affirm that they have found such on shell fish. Oysters are said to have insects witli many feet in them, and we fee evidently that the shells of sea snails and muscles have been eaten by worms.
Fishes though living constantly in water, and having their bodies covered with scales, are not exempt from the insults of insects; these attack the- most monstrous whale, as well as the smallest filh. Some harbour under the scales, as under a roof; others attach themselves near the very eyes* and adhere so strongly, that notwithstanding the rapidity of the hfh, it cannbt shake them off. Others insinuate themselves under the ears of whales, and arc there nourished; others pierce the flesh, and penetrate so deeply, that they cannot be seen or expelled. Some glide into the intestines which they pervade in all directions } or settle in the stomach.
Many authors have observed that insects harbour in the feathers of birds j not however always in equal numbers; for in autumn, there are fewer of them than at any other season. The cause 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 geese, are attack-ed by vermin, and this is perhaps the reason why hawks are so tormented with them. The birds they seize, communicate these vermin to them which they never can afterwards rid themselves of. If we may believe the testimony of authors, cranes have also a great number of insects adhering to them. The fame is to be said of Peacocks, and Turkies; but few birds are more cruelly infested with them than pheasants.to
sants. They would be eaten into the bone by vermin, were they not to dust themselves often, in order by this means to get rid of their troublesome lodgers. Storks and pidgeons are also very subject to them. It is said that there is a bird "in the Brazils, called Taputa, which consists of no:hing but ikin, and bone and vermin. These insects do not fix indifferently on all parts of the bird they adhere to; Some lodge under the (kin, particularly about the neck, where the bird cannot easily get at them with his bill 5 others on the quills of their feathers; others on the wings &c. An attentive observer with little trouble may easily convince himself of these facts.
Insects do not less infest quadrupeds than birds< The Gad-fly pierces the skin of cows, deer and hogs# and deposits its eggs; the larvæ afterwards nestle between the skin and the flesh. Some are found in the heads of various animals, but chiefly in those of the deer kind. To this some people have attributed the annual casting of their horns. They insinuate themselves also into the noses of different quadrupeds. Shepherds know but too well how fatal they are in this cafe to the sheep they attack. Some penetrate even to the intestines, and move there as if in I mg galleries. Such are found in the intestines of horses; but besides these, what vast numbers of insects attach themselves externally to quadrupeds? Some flies chiefly infest dogs, others horses. Different fpe-s cies of pediculi adhere firmly to the skins of. asies, dogs, horses, deer, sheep, &c*
Man the most noble of animals, is a world inhabited by multitudes of insects. The famous Borelli, an author who certainly is intitled to credit, affirms that he discovered in human blood animalcules of a figure similar to that of whaks, swimming in it, as
in in a red sea. Other writers, equally learned and curious^ mention larvæ found in the human brain, which proved fatal to some, tho' others were happily relieved from them. Insects likewise find their way into the human stomach, whence they are expelled by means of emetics. Our intestines, are not more exempt from them than those of other animals, as I had occasion to mention above. Our whole body, so to speak, is like a storehouse which furnishes food to an infinite number of infects. Some lodge between the skin and the flesh where they live at our expence. Young children who are not kept clean, are chiefly exposed to the attacks of vermin; and sometimes it has become necessary to make incisions in order to' extract them from the nose, the eye brows, the ears, and the tongues of many persons. There are sometimes animalcules under the skin of the hand, which creep along and make little elevations similar to those made in the earth by a mole. The Indians often have the leg and sole of the foot attacked by long worms which cannot be extracted without the greatest precaution. If they are broken, and the least part remain in the limb or in the foot, the life of the person becomes endangered. There is also in the Indies a small kind of flea called nigua (Pulex penefrans) which'is likewise exceedingly troublesome. It burrows between the nail and the flesh of the toes, making them swell to such a degree, that it is necessary to make an opening in them. One would think that the hardness of the bones would secure them from the insults of these animalcules; and yet some are found living and feeding there. It is needless to mention those that infest the external parts of our bodies, they are too. well known. I shall therefore stop for a moment to consider the wonderful discoveries made by Leewenhoeck in the semen of animals.
That illustrious observer of nature perceived WitrV his microscope an infinite number of small animals swimming in the spermatic liquor. This discovery made him conjecture that the strongest and most vi^ gorous of these animalcules -were arrested 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,*immediatelyafter its commerce with the male, he found in the matrix a vast number of these living animalcules.. The obser?ations he made on the semen of different persons seemed to make the thing eertain. 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 eld men some indeed were found, but they were without strength or vigour and almost dead. Lastly in people that were sterile, these animals were nor discovered^ or if they were discovered, they were dead.
But he carried hrs observations further, and thought he could distinguish the different sexes in these animalcules: whence he concluded that animals conceived males or females according as the different sexes were detained in the matrix, where they were fostered, and received enlargement.
These animalcules are exceedingly small, and Leewenhoeek say*, that a drop like a grain of sand con* tained many thousands of them. He found them smaller than those globules that give to blood its red colour, and he thinks that the place occupied by a grain of sand, might contain an hundred thousand. Their bodies are round; growing somewhat thick towards the head, and gradually diminishing towards the Kiil, which is five or fix times longer, and- about 6ve land -twenty times more slender than the rest of the body; it is likewise transparent. They bend it a little, and move themselves like eels in water. There is a very great difference between she young of these animalcules, and those that are come to maturity. The first have the body more slender, the tail three times shorter, and less pointed than the latter. In the semen of a ram, those animalcules swam in a string one. after another, as fneep do in water.
Many learned men have made the fame observations after Leewenhoeck. In this number are Huygens, Andry, Valisnieri, Wolff and Tummig. Cartheuser shewed these animalcules some years ago at Halle in his lectures on experimental philosophy to more than sixty persons. Hartsoeker examined, during a course of thirty years the semen of a vast number of quadrupeds and birds. He compares the spermatic animalcules of the first to the tadpoles frequent in stagnant waters, which have not yet got feet; those of birds resemble small worms or a very slender thread. These observations made him suppose that there were only two kinds of spermatic animalcules to wit, those of quadrupeds, and those of birds. He did not deny that there might be diversities according to the different species, especially between those of man and quadrupeds; but he said 1 hat these were not discernible on account of their minuteness and the velocity of their motions.
The defenders of this doctrine disagree when they come to explain how these animalcules contribute to the generation of the particular species of animal which has produced them. Some with Leewenhoeck believe that in the intercourse of viviparous animals, one or more of these animalcules attach themselves, ^o the matrix, that others serve for their food, and
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