DISEASES OF THE HEAET, BLOOD VESSELS, AND LYMPHATICS. 73 



carry dark-red blood. Tlie impure dark-red blood is collected from 

 the capillar}' vessels and carried to the right auricle by the veins; it 

 passes down into the right ventricle, and thence into the pulmonary 

 artery and through its branches to the capillaries of the lungs, where 

 the carbonic-acid gas and other impurities are given up to the air in 

 the air cells of the lungs (through the thin walls between the capilla- 

 ries and the air cells), and where it also absorbs from the air the 

 oxygen gas necessary to sustain life. This gas changes it to the 

 bright-red, pure blood. It passes from the capillaries to the branches 

 of the pulmonary veins, which convey it to the left auricle of the 

 heart ; it then passes through the auriculo- ventricular opening into 

 the left ventricle, the contraction of which forces it through the 

 common aorta into the posterior and anterior aortas, and through all 

 the arteries of the body into the capillaries, where it parts with its 

 oxygen and nutritive elements and where it absorbs carbonic-acid 

 gas and becomes dark colored. (See theoretical diagram of the 

 circulation, PI. VII.) 



The branches of certain arteries in different parts unite again after 

 subdi\iding. This reuniting is called anastomosing, and assures a 

 quot:'. of blood to a part if one of the anastomosing arteries should be 

 tied in case of hemorrhage, or should be destroyed by accident or 

 operation. 



THE BLOOD. 



The various kinds of food, after being digested in the alimentary 

 canal, are absorbed and carried into the blood by the lymphatics, and 

 by the blood to the places where nutrition is required. The blood 

 takes from all parts of the body all that is no longer required, and 

 carries it to the different organs through which it is eliminated 

 from the body. It contains within itself all the elements which 

 nourish the body. 



The blood may be considered as a fluid holding in solution certain 

 inorganic elements and having certain bodies suspended in it. To 

 facilitate description, the blood may be considered as made up of the 

 corpuscles and the liquor sanguinis. The corpuscles are of two kinds, 

 the red and the white, the red being the more numerous. The color 

 of the blood is caused by the coloring matter in the red corpuscles, 

 which are the oxygen carriers. Both kinds are very minute bodies, 

 which require the aid of the microscope to recognize them. The 

 liquor sanguinis is composed of water containing in solution salts, 

 albumen, and the elements of fibrin. 



The lymphatics, or absorbents, are the vessels which carry the 

 lymph and chyle in the blood. They begin as capillaries in all parts 

 of the body, gradually uniting to form larger trunks. Placed along 

 the course of the lymphatic vessels are glands, in some situations 

 collected into groups ; for example, in the groin. These glands are 



