ORGANS OF THE MAMMALIA. 109 



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. 



It is through the routine we have described, from the 

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

 ted, 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 oth- 

 er organ by which the chyle can be conveyed to the 

 blood, except the thoracic duct ; hence our lives con- 

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

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

 Without 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 

 muscular power, and we should soon fall away and die 

 of inanition, without the hope of a remedy. 



Circulation of the Blood. The blood is brought from 

 all parts of the system by the veins, which are constant- 

 ly enlarging by communications with each other, as they 

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

 the ascending and descending vence caves. These con- 

 vey 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 atmos- 

 phere. 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. 



This however, is only a general account of the circu- 

 lation ; a more particular one being reserved, until we 

 come to treat of the circulation in different orders of an- 

 imals, 



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

 10 



