10 



CHAPTER II. 



Blood. 



heart and blood-vessels circulation of blood blood 



• coagulation of blood nutrition and waste distribu- 

 tion of blood in the body anemia congestion inflam- 

 mation repair after inflammation counter-irritation — • 



bleeding. 



HEART AND BLOOD-VESSELS.— The heart (Fig. 3), which is a hollow 

 mu>cle, is divided by a longitudinal partition into two independent parts, 

 namely, the right side and the left side. Each of these is separated into two 

 compartments (an auricle and a ventricle) by a valve, which, under conditions 

 of health, allows fluid to flow from an auricle into the ventricle of its own side ; 

 but does not permit it to go in the opposite direction. The heart is of a more 

 or less conical shape, with the apex pointing downwards. The auricles, which 

 are much smaller than the ventricles, occupy the base, and the ventricles the 

 remainder of the heart. The left ventricle opens into the aorta, which is the 

 largest of all the arteries, and which, shortly after leaving the heart, splits 

 up into branches that distribute their still smaller ramifications to every part 

 of the body, and finally terminate, as a rule, in capillaries. In Fig. 

 3, the aorta and its branches, the pulmonary arteries, the veins of general 

 c'.rculation and the pulmonary veins are respectively shown, for con- 

 venience sake, as consisting of a single trunk. The capillaries are found in 

 countless numbers throughout the entire system. These minute tubes have 

 extremely thin walls, are about -^^^^^ of an inch in dian eter, and proba1)ly 

 do not exceed ^^'tj of an inch in length. They open into the ve'ns, which are 

 very small at first ; but gradually uniting with each other, enter the right 

 auricle by two large branches, and a few small ones. The right 

 auricle communicates, as I have already said, by a valve with the right 

 ventricle, which opens into the pulmonary artery. This artery proceeds to 

 the lungs, and becomes split up in.to branches and finally into capillaries that 

 spread themselves through the air-cells of the lungs. These air-cell capillaries 

 unite to form the pulmonary veins, which open into the left auricle. 



CIRCULATION OF BLOOD.— Each side of the heart acts like one of 

 those india-rubber pumps which, when dilated, becomes filled with fluid by 

 means of a tube at one end, and which, when squeezed by the hand, drives 

 the contained fluid through a tube at the other end, on account of the pres- 

 ence of a valve preventing its return through the tube by which it entered 

 the bulb. Here, the tube of entrance is the veins and the auricle ; the bulb, 



