A Treatise on Domestic Economy; For the Use of Young Ladies at Home and at School

When the blood reaches the lungs, and is exposed to the action of the air which we breathe, it throws off its impurities, becomes bright in color, and is then called arterial blood. It then returns to the left side of the heart, (on the right of the engraving,) by the pulmonary veins E, E, (also seen at _m_, _m_, Fig. 15,) into the left auricle F, whence it is forced into the ventricle, G. From the left ventricle, proceeds the _aorta_, H, H, which is the great artery of the body, and conveys the blood to every part of the system. I, J, K, are branches of the aorta, going to the head and arms. [Illustration: Fig. 14.] Fig. 14, represents the heart, with its two sides united as in nature; and will be understood from the description of Fig. 13. On the opposite page, Fig. 15, represents the heart, with the great blood-vessels, on a still larger scale; _a_, being the _left ventricle_; _b_, the _right ventricle_; _c_, _e_, _f_, the _aorta_, or great artery, rising out of the left ventricle; _g_, _h_, _i_, the branches of the aorta, going to the head and arms; _k_, _l_, _l_, the _pulmonary artery_, and its branches; _m_, _m_, _veins of the lungs_, which bring the blood back from the lungs to the heart; _n_, _right auricle_; _o_, _vena cava inferior_; _p_, veins returning blood from the liver and bowels; _q_, the _vena cava superior_; _r_, the _left auricle_; _s_, the left _coronary artery_, which distributes the blood exclusively to the substance of the heart. [Illustration: Fig. 15.] ORGANS OF DIGESTION AND RESPIRATION. Digestion and respiration are the processes, by which the food is converted into blood for the nourishment of the body. The engraving on the next page (Fig. 16) shows the organs by which these operations are performed. In the lower part of the engraving, is the stomach, marked S, which receives the food through the _gullet_, marked G. The latter, though in the engraving it is cut off at G, in reality continues upwards to the throat. The