80 MANUAL OF CATTLE-PEED ING. 



and anterior part of the Ibodj, the nutrients which a3*e resort- 

 ed by the lacteals are poured just before it enters the heart. 



The passage of the blood from the left heart through 

 the body and back to the right heart, is called the greater 

 or systemiG circulation ; that from the right heart through 

 the lungs to the left heart the jmlmonary circulation. 



The appearance of the blood in the veins and arteries 

 is strikingly different. In the veins it has a dark, cherry- 

 red color, but after it has passed through the lungs and is 

 sent out by the heart into the arteries it has a bright, 

 scarlet color. The former is called venous, the latter arte- 

 rial blood. An exception to this rule, that the arteries 

 carry bright-red blood and the veins dark, is found in the 

 pulmonary circulation, where, of course, the vessels leading 

 from the right heart to the lungs carry venous blood, and 

 those leading from the lungs to the left heart, arterial. 

 Nevertheless, the general nomenclature is adhered to, and 

 the former are called arteries and the latter veins. Arteries 

 conduct the blood from the heart, veins towa/rd it. 



§2. Respiration. 



Under respiration we here include not only the act of 

 breathing, but all those chemical changes in the body of which 

 that act is partly the cause and partly the consequence. 



The Iiungs. — The principal organs of respiration are 

 the lungs, which, with the heart, occupy the cavity of the 

 chest. This cavity is enclosed on the sides by the ribs, 

 and is separated from the abdominal cavity, containing the 

 digestive organs, by a strong, ai-ched, muscular partition, 

 the diaph/ragm. The diaphragm is convex toward the 

 chest, and by its contraction and a simultaneous outward 

 motion of the ribs, caused by muscles situated between 

 thetn, the size of the chest cavity is enlarged, and air 



