34 MANUAL FOR STABLE SERGEANTS. 



accompany arteries, as a rule, and bear the same names; among 

 exceptions to this rule may be noted the anterior and posterior vena 

 cava and the jugular veins. The circulation through the veins is 

 assisted by the contraction of the muscles during movement and 

 respiration. 



71. The blood is a fluid which carries oxygen and nutritive 

 material to all the tissues of the body and, together with the lymph, 

 carries the waste material to the excretory organs. It is an opaque, 

 thickish fluid with a salty taste. Its color varies, being a bright red 

 or scarlet in the arteries and a dark purple in the veins, except in the 

 pulmonary artery, which carries purple or venous blood, and the 

 pulmonary veins, which carry red or arterial blood. It forms a 

 clot when the blood vessels are ruptured and the blood is exposed 

 to the air or tissues. 



72. Blood is composed of serum and red and white corpuscles. The 

 serum is a thin, yellovoish fluid in which the corpuscles float. It con- 

 tains the soluble nutrient material from the food. 



73. The red corpuscles carry oxygen to the tissues and carbonic 

 acid gas away from them.- When they are charged with oxygen they 

 give the scarlet color to the blood, and the purple color when charged 

 with carbonic acid gas. The red corpuscles are iormed in the bone 

 marrow. 



74. The white corpuscles repair and assist in replacing worn out, 

 diseased or injured tissues. They also protect the tissues by destroy- 

 ing the germs which produce disease. They are formed in the 

 lymphatic glands and the spleen. 



75. There are two divisions of the circulation, the pulmonary 

 and the systemic. 



(a) The pulmonary circulation takes the blood from the heart to 

 the lungs and back to the heart. The impure blood from the whole of 

 the body enters the right atrium by the anterior and posterior venae 

 cavae; from the right atrium it passes to the right ventricle; from the 

 right ventricle it is pumped through the pulmonary artery to the lungs, 

 where it is purified by giving off carbonic acid gas and taking up oxy- 

 gen. From the lungs the now purified blood is returned to the heart 

 through the pulmonary veins and emptied into the left atrium. 



(6) The systemic circulation. From the left atrium the blood passes 

 into the left ventricle, thence into the aorta to be pumped to all parts 

 of the body, being distributed by means of arteries and capillaries; 

 from the capillaries it is collected by veins and brought back to the 



