ORGANS OF THE MAMMALIA. 105 



glands in all parts of the system, with the "purple fluid 

 from which all the various secretions are produced. By 

 these processes, vegetable as well as animal matter, is 

 converted into flesh. 



300. It is through the routine we have described, from 

 the mouth to the subclavian vein, that the system is reno- 

 vated, and the exhaustion consequent upon the exercise of 

 all its numerous functions, is constantly repaired, and the 

 whole system kept in vigor and health. Not a particle 

 of nourishment can be added to the circulation until the 

 food has been changed into chyle ; nor is there any other 

 organ by which the chyle can be conveyed to the blood, 

 except the thoracic duct ; hence our lives constantly 

 depend on a little stream of chyle, about the size of a 

 crow-quill, which enters a vein under the arm-pit. With- 

 out this source of renovation, the mass of blood would 

 soon become deficient in quantity and quality ; there 

 would be no remedy for exhaustion, no source of muscu- 

 lar power, and we should soon fall away and die of inan- 

 ition, without the hope of a remedy. 



301. Circulation of the Blood. The blood is brought 

 from all parts of the system by the veins, which are con- 

 stantly enlarging by communications with each other, as 

 they approach the heart. The veins v, v, Fig. 74, are 

 called the ascending and descending vence cavce. These 

 convey the blood to the right auricle of the heart, u. 

 When the auricle is full, it contracts, and sends the blood 

 to the right ventricle h. From the right ventricle, it is 

 thrown by the strong contraction of the heart, to the 

 lungs, where it is exposed to the influence of the atmo- 

 sphere. It is then brought to the left auricle of the heart, 

 which contracting, throws it into the left ventricle, the 

 action of which forces it through the aorta, to all parts 

 of the system, to be returned again to the right auricle 

 by the veins, as before. 



302. This, however, is only a general account of the 

 circulation ; a more particular one being reserved, until 

 we come to treat of the circulation in different orders of 

 animals. 



What is said of the importance of the chyle to the living system? 



