Human physiology : designed for colleges and the higher classes in schools and for general reading . ns to the heart, it is sent by the heart tothe lungs, in order to be exposed to the air before it is sentagain over the system. For this purpose there are two circula-tions, and the heart is a double organ; or rather, there are ineffect two hearts for the two circulations, for the two sides ofthe heart have no communication with each other. The appa-ratus for all this is very complicated, but I think it can be madeclear to you. 113. I present, first, a diagram, which is intended to repre-sent m
Human physiology : designed for colleges and the higher classes in schools and for general reading . ns to the heart, it is sent by the heart tothe lungs, in order to be exposed to the air before it is sentagain over the system. For this purpose there are two circula-tions, and the heart is a double organ; or rather, there are ineffect two hearts for the two circulations, for the two sides ofthe heart have no communication with each other. The appa-ratus for all this is very complicated, but I think it can be madeclear to you. 113. I present, first, a diagram, which is intended to repre-sent merely the course of the circulation, without regard toproportionate size, or to minutiae in the arrangement of the ap-paratus. Let a represent the right side of the heart, c the leftside, b the lungs, and d the general system of the body. Thearrows show the direction in which the blood flows. In all theshaded part the blood is venous or purple, and in the part notshaded it is arterial or red. We will now take some point ofbeginning, and trace on the Figure the course of the circulation. FIG. DIAGRAM SHOWING THE COURSE OF THE CIRCULATION. We will start at a, the right side of the heart. The blood re-ceived here, of a purple color, from the whole body by theveins is sent by the heart to b, the lungs. Here it changes tored blood, and passes by veins back to the heart—but, observe,it is to the left side of the heart, c. It is now sent by this lefthalf of the heart to all parts of the system, represented by , in the capillaries, it is changed to purple blood, and goesback by veins to the light side of the heart, a, the place where we started. 1 74 HUMAN PHYSIOLOGY. Two circulations and two hearts. Arrangement of valves. 114. You see, then, that there are two separate circulations,one through the general system, and the other through the lungsalone. In both circulations the blood is sent from the heartby arteries, and is brought back to it by veins. But notice that,while
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