The blood, now laden with the products of digestion, passes from the venous capillaries of the stomach and intestines to the blood vessels of the mesentery. These pour their contents into a large vessel called the portal vein, which conducts the blood direct to the liver. It will thus be seen that by this arrangement the albumose derived from albuminous foods, the glucose derived from the starch and sugar, together with the various salts held in solution, are carried direct to the liver by the portal vein, there to be elaborated into the substances necessary for nutrition. The glucose is converted by the action of the liver cells into glycogen, and is, it is asserted, ultimately restored to the circulation in the form of glucose, to be probably burnt up in the tissues in the processes of metabolism or tissue change. The albumose is, after passing through the liver, returned to the circulation in the form of blood albumen.

Most of the fatty particles of the food are absorbed by the lacteals, and enter the general current of the circulation by the thoracic duct, which pours its contents into the left jugular vein. The jugular vein leads into the superior vena cava, which conducts the blood to the right side of the heart, from which it is pumped by the pulsation of the heart into the lungs. In the lungs the fatty particles with which the blood is charged after a meal entirely disappear, and are probably burnt up in the process of the maintenance of the body heat.