1G0 NORMAL HISTOLOGY. 



elaborating the bile and discharging it into the duodenum. But. 

 the bile has more than one purpose. It aids in the digestion and 

 absorption of food, and it also contains excrenientitious matters 

 destined to leave the body through the alimentary tract. Even the 

 secretory function of the liver, therefore, serves a double purpose : 

 the supply of substances useful to the organism and the elimina- 

 tion of products that would be detrimental if retained. 



But the function of the liver is not confined to the elaboration 

 of the bile. It also acts as a reservoir for the storage of nourish- 

 ment, which can be drawn upon as needed by the organism. This 

 is the meaning of the glycogen and fat which have infiltrated the 

 cells. 



The food-materials that are absorbed from the digestive tract pass 

 into the system through two channels : the lymphatic and the portal 

 circulations. The latter carries them to the liver, where some of 

 the fat, probably after desaponifieation, is taken up by the epithelial 

 cells, which also appropriate a portion of the sugar in the portal 

 blood, transforming it into glycogen and holding it in that form 

 until a relative deficiency of glucose in the blood reveals its need 

 by the system. 



The blood comes into such close relations with the epithelial cells 

 of the liver that an interchange of soluble substances between them 

 appears to be about as easy a matter as the interchange of gases 

 between the blood and the air in the lungs; and, as in the latter 

 case, this interchange is mutual : some matter passing from the 

 blood to the liver-cells and some from the cells to the blood. In 

 the lung there is a gaseous regeneration of the blood ; in the liver, 

 a renovation as to certain of its soluble constituents. 



The Gall-bladder. — The bile is secreted continuously by the liver, 

 for it is an excrement ; but it is discharged intermittently into the 

 alimentary tract, as required by the digestive processes. In the 

 interval it is stored in the gall-bladder. 



The gall-bladder is lined with columnar epithelium, capable of 

 secreting mucus. Beneath this is a layer of fibrous tissue, which 

 becomes areolar and supports the chief bloodvessels and lymphatics. 

 A few glands opening into the gall-bladder are occasionally present 

 in this tissue. Beneath this is the wall of the organ, composed of 

 interlacing bands of fibrous and smooth muscular tissues. The sur- 

 face is invested by a portion of the peritoneum. The excretory bile- 

 duct has a similar structure. 



