But other exchanges take place. The blood, in addition to oxygen and carbon, contains hydrogen and nitrogen. But it contains its four elements in various forms of combination, producing the following materials for the use of the body: of 1,000 parts of blood, about 779 are water; 141 are red globules; 69 are albumen; 3 are fibrin; 2 are fatty matter; 6 are various salts.
Albumen and fibrin are a kind of flesh imperfectly formed, and probably are chiefly used in repairing the muscles. The red corpuscles contain the oxygen which goes to combine with the superabundant carbon, and develop heat; the fatty matters probably repair the fatty tissues, and glands that are of a fatty nature; and the various salts contribute to the bones, and to the chemical properties of those secretions which are formed by the glands, &c., while the great proportion of water is employed in cleansing, softening, and cooling the whole, or the living edifice, and it is the medium through which all the nutrition of the body is distributed.
900. Why do we feel the pulse beat?
Because every time that the heart contracts it send a fresh supply of blood to the blood-vessels, and the motion thus imparted creates a general pulsation throughout the system: but it is more distinctly perceived at the pulse, because there a rather large artery lies near to the surface.
"Thy hands have made me and fashioned me: give me understanding, that I may learn thy commandments."—Psalm cxix.
901. What becomes of the matter collected by the blood in the course of its circulation?
We have already explained that carbon is thrown off from the lungs in the form of carbonic acid gas. But there are many other matters to be separated from the venous blood, and its purification is assisted by the action of the liver, which is supplied with a large vein, called the portal vein, which conveys into the substance of the liver, a large proportion of the venous blood, from which that organ draws off those matters which form the bile, and other matters which are transmitted with the bile to the bowels. The liver and the lungs, therefore, are the great purifiers of the venous blood. But there are also smaller organs that assist in the same work.