Skin, Pores of the. Each part of human skin is filled with excretory conduits or pores that continually expel superfluous humors of the fluid that circulates. To see these pores, one must cut a piece of the exterior skin , as thin as possible, with a well-sharpened razor; immediately after, you will cut from the same place a second piece that you put under a microscope; and in a part that will not be bigger than a grain of sand, you will perceive a countless number of pores as clearly as you would be able to distinguish as many little holes formed by a fine needle on paper, if you held it up to the sun. The flakes of the epidermis prevent one from distinctly seeing the pores, unless one separates them with a knife, or cuts them in the preceding manner; but if one prepares in this manner a piece of skin that is between the fingers or on the palm of the hand, and if one examines it with a microscope, one will see with pleasure, light through the pores.

Mr. Leeuwenhoëck tries to give some idea of the incredible number of pores on the human body. He supposes that there are 120 pores in a line, that is only a 10 ^th of a thumb; however in order to not be too cramped, he only calculates 100 on the foot; a thumb length will therefore contain a thousand, and a foot, twelve thousand; according to this calculation, a square foot will contain one hundred forty-four million, and supposing that a medium-sized man’s surface is made of fourteen square feet, there will be on his skin 2,016,000,000 pores.

In order to have yet a clearer notion of the prodigious number of pores, by the idea that we have of time, suppose along with Father Mersenne, that each hour is composed of 60 minutes, each minute of 60 seconds or 60 beats of an artery; therefore in an hour there are 3600 beats, in 24 hours 86400, and in a year 31536000; but there are about 64 times as many pores in the surface of the skin of a man, and consequently, it would be necessary that he live 64 years in order to have only one single beat for each pore of his skin .

Doctor Nathaniel Grew observes that the pores by which we sweat are more remarkable in particular on the hands and on the feet; for if one washes his hands well with soap, and if one examines with an ordinary glass the palm of the hand or the extremities, and the first joints of the thumb and the fingers, one will find there an infinite number of parallel grooves between them, of equal size, and at equal distances. Excellent eyesight will perceive the pores in straight lines on these grooves, without a glass; but if one observes them with a good glass, each pore will seem like a small fountain, with the sweat that transpires from it crystal clear; and if one rubs it, one will see another drop immediately exit.

In reflection of this multitude of orifices above the skin , we have reason to believe that small insects, like fleas, lice, gnats, etc. do not make new openings with their sharp instruments, but they only introduce them into the vessels of the skin to suck out the blood and other humors that serve as nutrition for them.