104 ANIMAf. FUNCTIONS. 



which tnere proceeds a tube called the thoracic duct, 

 which conveys the chyle to the circulation ; /, is a portion 

 of the liver. That portion of the heart, h, which is 

 marked u, is called the auricle, while the cavity, h, is 

 called the ventricle, a is the aorta, which is the trunk of 

 the largest artery, and v, v, v, are the large veins which 

 convey the blood to the heart. The part b, is a portion of 

 the lungs. 



296. Having pointed out the different parts, we will 

 next explain in few words, the different processes by which 

 food is changed iilto blood, and also the course of the 

 blood in its circulation. 



297. The food being masticated and mixed with the 

 fluid secretions of the mouth, is then collected into a 

 mass by the muscles of the cheeks and tongue, and swal- 

 lowed, being carried along the tube o, by its contractions, 

 down to the stomach s. There it is mixed with a fluid 

 secretion of the stomach, called the gastric juice, and by 

 which it is dissolved and prepared to afford -chyle after it 

 has been conducted through the pylorus. After having 

 passed the pylorus p, the food is mixed with the bile, a 

 bitter secretion from the liver, and also with a fluid from 

 the pancreas, when a portion is elaborated into chyle, and 

 is ready for absorption into ihe-lacteals, which are the ves- 

 sels spread over the mesentery, like a net-work, as shown 

 by the figure. 



298. The chyle being taken up by the lacteals, the 

 mouths of which are thickly spread over the interior of the 

 intestinal tube, is carried by many branches to the recep- 

 tacle of the chyje, r, from which it is conveyed by the 

 thoracic . duct, t, to one of the large veins under the arm, 

 called the subclavian vein, and by this vein to the heart. 

 It thus gains admittance to the general circulation of the 

 blood, and by a process which we cannot explain becomes 

 blood itself. 



299. It is by means of a constant reception of chyle 

 into the circulation, that the quantity of blood continues 

 undiminished ; and that the arteries are enabled to furnish 



Explain Fig. 74, and point out the name and situation of each part, as 

 designated by the letters. In what part of the system is the chyle thrown 

 into the circulation ? 



