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fants. They would be eaten into the bone by vera min, were they not to dust themselves often, in ora der 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 nothing but ikin, and bone and vermin. The& insects do not fix in. differently on all parts of the bird they adhere to. Some lodge under the feing particularly about the neck, where the bird cannot easily get at them with his bill ; others on the quills of their feathers ; 0. thers on the wings &c. An attentive observer with little trouble may easily convince himiclí vf these facts.
· Insects do not less infeít quadrupeds than birds. The Gad-fly pierces the skin of cows, deer and hogs, and depolits its eggs; the larvae afterwards nelle between the skin and the fun. 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 insinuaie themselves also into the noses of different cuádrupeds. Shepherds know but too well how fatal they are in this case to the fhuip they attack. Some penetrate even to the intestines, and move there as if in long galleries. Such are found in the intestines of hor. fes ; but besides these, what yait ;umbers of insects attach themselves externally to quadrupeds ? Some flies chiefly infest dygs, others hori.. Difereni spe. cies of peticuli adhere firmly to the skins of afies, dogs, horses, leer, iheep, C.
Man the most noble of animals, is a world inha. bited by multitudes of infects. The famous Borelli, an author who certainly is intitled to credit, afirms that he discovered in human blood animalcules of a figure similar to that of whalus, swimining in it, as
in a red fen. Other writers, equally learned and curious; mention larvae found in ihe human brain, which proved fatal to fome, ho' 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 insects. Some lodge between the ikin 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 fule of the foot attacked by long worms which cannot be extracted without the greate est 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 penetrans) which is likewise exceedingly troublesome. It burrows between the nail and the flesh of the toes, making them iwell to such a degree, that it is necesfary 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 insert the external parts of our bodies, they are too well known, I shall therefore stop for a moment to consider the wonderful disco. veries made by Leewenhoeck in the semen of ania mals.
That That illustrious observer of nature perceived with his inicroscope 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 fætus. 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 vast number of these living animalcules. The observations he made on the sea men of different persons seemed 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 some indeed were found, but they were without strength or vigour and almost dead. Lastly in people that were sterile, these animals were not discovered, or if they were discovered, they were dead.
But he carried his 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 fexes were detained in the matrix, where they were fostered, and received enlargement.
These animalcules are exceeding'y smail, and Lee. wenhoeck says, 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 fard, might contain an hundred thousand, Their bodies are round, growing somewhat thick towards the head, and gradually diminishing towards the tail, which is five or fix tinies longer, and about
five and 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 the young of there animalcules, and those that are come to maturity. The first have the body more slender, the tail three times forter, and lets pointed than the latter. In the semen of a ram, those ani. malcules swam in a string one after another, as sheep do in water,
Many learned men have made the same observations after Leewenhoeck. In this number are Huy. gens, Andry, Valisnieri, Wolff and Tummig. Car. theuler shewed these animalcules fome years ago at Halle in his lectures on experimental philofophy to more than sixty persons. Hartfoeker 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 fre. quent in stagnant waters, which have not yet got feet; those of birds resemble small worms or a very slender thread. Thele observations nade him suppose that there were only two kinds of spermatic aniinalcules to wit, those of quadrupeds, and those of birds. He did not deny that there might be diversities accord. ing to the different species, especially between chofe of man and quadrupeds; but he said that 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 contribuie 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, to the matrix, that others ferve for their food, and L 2
that at last they become a perfect fætus. They add that the ova in the ovarium, only produce the se. cretion of certain fluids. In oviparous animals the egg answers the end of the matrix, and to it the animals cule attaches itself. It penetrates into the middle of the yolk where it gradually grows to its periection. Other authors dissent from this syslem, 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 state to receive them, by means of an aperture furnithed with a valve which prevents their retreat. in this egg it is nourished and grows. Lastly, some authors affirm that these animalcules have not yet the figure of a fætus, and that they receive it by a transformation similar to that of a caicrpillar changing into a butterfly.
I shall not venture to decide on these various opi. nions, or to determine whether the animalcules are necessary to procure conception, whether they serve only to cause a voluptuous tiulation, or if they are destined to any other use; still less will I supporí the opinion I have detailed. It appears to me too fingu. lar, and liable to too many difficulties, as various au. thors have shewn. It is certain, however, that these spermatic animalcules are worms of a particular kind, destined by the Creator to serve a particular purpose; but inan' has not yet discovered that destination, so great is the imperfection of human knowledge.
I had almost forgot to inention that infedts are found in the dry remains of plants and animals, as well as in works of art. There are some dry legumes wbich have the shell as hard as that of a nut : but This hardness does not secure them from the piercing tech of fomc inicis which reduce thein to powder.