INTERNAL ORGANS. 9 



nishing the various parts with the vital prin- 

 ciple; the latter conveying back the blood, 

 thus deprived of its essential parts, to the 

 heart, that it maybe renovated by circulating 

 through the lungs, as we shall now describe 

 more particularly. When the left ventricle 

 is full of blood, it contracts so powerfully as 

 to force its contents into the aoi'ta or o-rand 

 artery, by which the blood is distributed all 

 over the body; it is then taken iip by the 

 veins, and conveyed by them into the iHght 

 auricle, whence it flows into the right ven- 

 tricle ; this also, when it is sufficiently dis- 

 tended, contracts upon its contents, and pro- 

 pels the blood into the pulmonary artery, by 

 which it is conveyed to every part of the lungs. 

 The pulmonary veins then receive it, and 

 convey it to the left auricle, whence it is 

 propelled into the left ventricle, that it may 

 again be distributed by the aorta to every 

 part of the body. 



The blood is thus conunually circulatino- 

 through the body ; and this process may be con- 

 sidered as one of the most important actions 

 that is performed in the animal machine. If it 

 be stopped for a few seconds, all motion is sus- 

 pended ; and if it be prevented a lonsrer time 



B 5 



