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_. [Verse: "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. [Illustration: Fig. 53.--SHOWING THE DISTRIBUTION OF BLOOD THROUGH BRANCHES OF THE AORTA.] A. The _aorta_. B. Branches given off for the _aorta_ to supply one portion of the intestines. C. Branches given off by the aorta to supply other portions of the intestines. A complete communication may be traced between these vessels from the origin of one to that of the other. D. The _pancreas_, or sweetbread, a large gland that forms the pancreatic juice, which it pours in through the duct. (_See_ Fig. 50.) E E E. The _large intestines_, forming the termination of the alimentary canal. CHAPTER XLIV. 902. _Why when we cut our flesh does it heal?_ Because the blood coagulates over the cut, and throws out a kind of _lymph_, which forms an incipient flesh, and excludes the air while the blood-vessels are engaged in _repairing the part_.