DISKASBS OF THB CIRCXJIyATORY ORGANS. 95 



valves, but consist of three layers. The inside one forms a smooth sur- 

 face for the blood to pass over, the outside one an elastic layer, while be- 

 tween them is a muscular layer which regulates the amount of blood re- 

 ceived by each part. This coat is necessary, as it is luanifest that the 

 heart cannot regulate the supply of blood sent to each portion of the 

 body. 



Capillaries. The capillaries are interposed between the ends of the 

 arteries and the beginning of the veins and not only carry blood, but, 

 owing to the construction of their walls, they enable the blood to come 

 in intimate relations with the tissues. By the blood thus coming so in- 

 timately connected with the tissue, it is enabled to deposit nourishment, 

 give up its oxygen, and lake in return what has been chemically united. 

 They take from the blood the nourishment, and give it off as a fluid 

 known as lymph, whose function is to irrigate and nourish. 



Veins. In most veins are valves which flap back against the side as 

 the blood flows onward toward the heart. Thus the blood cannot be 

 forced backward by any cause. The walls of veins are not so thick, 

 strong, or elastic as are those of the arteries — the strength and elasticity 

 not being needed, as the blood simplj^ flows through the veins and is not 

 forced through as it is in the arteries. The blood is aided in its course 

 through the veins by a contraction of the voluntary muscles, indirect 

 action of the valves in the veins, and by suction produced by the move- 

 ments of the thorax in breathing. 



Pulse. At certain portions of the body arteries come near the sur- 

 face. If the finger be placed over these blood-vessels a beating can be 

 felt. These beats are caused by the heart forcing the blood into the 

 arteries. Each pulse represents a heart beat. 



Character of the Pulse. This has been described under the 

 chapter DISEASES OF THE CIRCUEATORY ORGANS. 



INFLAMMATORY DISEASES OF THE HEART. 



General Structures. There are three parts to the heart that are 

 liable to inflammation. From the names of these structures the names of 

 the diseases are derived. Myocardium is the muscular structure of the 

 heart; endocardium is the serous membrane lining the heart; and peri- 

 cardium is the sac surrounding the heart. 



Myocarditis. An inflammation of the muscular structure of the 

 heart. This is rarely detected without being connected with inflamma- 

 tion of the endocardium or pericardium. The causes are over-exertion 



