110 



THE CHRISTIAN PHILOSOPHER. 



veins. The heart is enclosed in the pericardium, 

 B. membranous bag, which contains a quantity 

 of water, or lymph. This water lubricates the 

 heart, and facilitates all its motions. The heart 

 is the general reservoir of the blood. When the 

 heart contracts, the blood is propelled from the 

 right ventricle into the lungs, through the pulmo 

 nary arteries, which, like all the other arteries, 

 are furnished with valves that play easily for 

 ward, but admit not the blood to return toward 

 the heart. The blood, after circulating through 

 the lungs, and having there been revivified by 

 coming in contact with the air, and imbibing a 

 portion of its oxygen, returns into the left auricle 

 of the heart, by the pulmonary vein. At the 

 same instant, the left ventricle drives the blood 

 into the aorta, a large artery which sends off 

 branches to supply the head and arms. Another 

 large branch of the aorta descends along the in 

 side of the back-bone, and detaches numerous 

 ramifications to nourish the bowels and inferior 

 extremities. After serving the most remote ex 

 tremities of the body, the arteries are converted 

 into veins, which, in their return to the heart, 

 gradually unite in to larger branches, till the whole 

 terminate in one great trunk, called the vena 

 cava, whicli discharges itself into the right au 

 ricle of the heart, and completes the circulation. 

 Each ventricie of the heart is reckoned to con 

 tain about one ounce, or two tabiespoonsfull of 

 blood. The heart contracts 4000 times every 

 hour; and, consequently, there passes through 

 it 250 pounds of blood in one hour. And if the 

 mass of blood in a human body be reckoned at 

 an average of twenty-five pounds, it will follow 

 that the whole mass of blood passes through the 

 heart, and consequently through the thousands 

 of ramifications of the veins and arteries, four 

 teen times every hour, or about once every four 

 minutes. We may acquire a rude idea of the 

 force with which the blood is impelled from the 

 heart, by considering the velocity with which 

 water issues from a syringe, or from the pipe of 

 a fire-engine. Could we behold these rapid mo 

 tions incessantly going on within us, it would 

 overpower our minds with astonishment, and 

 even with terror. We should be apt to feel 

 alarmed on making the smallest exertion, lest 

 the parts of this delicate machine should bo 

 broken or deranged, and its functions interrupted. 

 The arteries, into which the blood is forced, 

 branch in every direction through the body, like 

 the roots and branches of a tree ; running through 

 the substance of the bones, and every part of the 

 animal frame, till they are lost in such fine tubes 

 as to be wholly invisible. In the parts where 

 the arteries are lost to the sight, the veins take 

 their rise, and in their commencement are also 

 imperceptible. 



Respiration, The organs of respiration are 

 the lungs. They are divided into five lobes; 

 three &amp;gt;f which lie on the right, and two on the 



left side of the thorax. The substance of the 

 lungs is chiefly composed of infinite ramifica 

 tions of the trachea, or windpipe, which, aftei 

 gradually becoming more and more minute, ter 

 minate in little cells, or vesicles, which have a 

 free communication with one another. At each 

 inspiration, these pipes and cells are filled with 

 air, which is again discharged by expiration. 

 In this manner, a circulation of air, which is ne 

 cessary to the existence of men and oiher ani 

 mals, is constantly kept up as long as life re 

 mains. The air-cells of the lungs open into the 

 windpipe, by which they communicate with the 

 external atmosphere. The whole internal struc 

 ture of the lungs is lined by a transparent mem 

 brane, estimated at only the thousandth part of 

 an inch in thickness ; but whose surface, from 

 its various convolutions, measures fifteen square 

 feet, which is equal to the external surface of the 

 body. On this thin and extensive membrane 

 innumerable veins and arteries are distributed, 

 some of them finer than hairs ; and through these 

 vessels all the blood of the system is successively 

 propelled, by a most curious and admirable me 

 chanism. It has been computed, that the lungs, 

 on an average, contain about 280 cubic inches, 

 or about five English quarts of air. At each 

 inspiration, about forty cubic inches of air are 

 received into the lungs, and the same quantity dis 

 charged at each expiration. On the supposition 

 that 20 respirations take place in a minute, it 

 will follow, that, in one minute we inhale 800 

 cubic inches ; in an hour, 48,000 ; and in a day, 

 one million, one hundred and fifty-two thousand 

 cubic inches a quantity which would fill seventy- 

 seven wine hogsheads, and would weigh fifiv- 

 three pounds troy. By means of this function, 

 a vast body of air is daily brought into contact 

 with the mass of blood, and communicates to it 

 its vivifying influence; and, therefore, it is of 

 the utmost importance to health, that the air, of 

 which we breathe so considerable a quantity, 

 should be pure, and uncontaminated with nox 

 ious effluvia. 



Digestion. This process is performed by the 

 stomach, which is a membranous and muscular 

 bag, furnished with two orifices. By the one, it 

 has a communication with the gullet, arid by the 

 other, with the bowels. The food, after being 

 moistened by the saliva, is received into the sto 

 mach, where it is still farther diluted by the 

 gastric juice , which has the power of dissolving 

 every kind of animal and vegetable substance. 

 Part of it is afterwards absorbed by the lymphatic 

 and lacteal vessels, and carried into the circulat 

 ing system, and converted into blood for supply 

 ing that nourishment which the perpetual waste 

 of our bodies demands. 



Perspiration is the evacuation ofthejuir.es of 

 tne body throu&amp;lt;;h the pores of the skin. It has 

 been calculated that there are above three hundred 

 thousand millions of pores in the glands of th 



