পাতা:পদার্থবিদ্যাসার.djvu/৮৯

78 and as long as this continues, we live. By the former the blood is brought in, and by the latter sent forcibly out into a duet, called the great artery. It is supposed the pulsations of the heart, in an infant, are more than six ibousand every hour, whether it takes or sleeps. In a fail-growth person, the number is more than four thousand. Pup. i anm mot siue thar i quite iiwdei siand what is meant by the circulation of the blood. Tut. It comprehends the whole course of the blood, as well in the lungs as ia the arteries and veius; and it is justly manted a circusation, because tlie bloed is perpetually passius round in the same tract. Pup. And you have said that blood is formed of the chy le ? Tui. 11 is: the chylc, w hiel, is the last change the foot; tı, fergoes previously to its conversion into blood. is conveyed tuto the thoracic duct. which opens into a large win, that carries it. with the blood comiuı: from the extremities, in; o the heart, tİıt nce through the sungs into the searl again. i’isp. What happens next Tut. This satue blood having passed through the Jungs, is forced from the ineart to all parts of the body, to the most minute raulisications: there it meets with veins to bring it back to the heart. Pup. \\ hy is it necessary that iiie blood from the veins should in every circulation pass through the lungs Tut. Because by this means the venous blood, which has lost some of its properties, is by its exposure to the atmosphere changed into arterial blood again, and thus becomes fitted for its functions.