346 MANUAL OF ZOOLOGY sect. 



duct, the bile duct, conveys its secretion, the bile, into 

 the most anterior part of the intestine known as the duo- 

 denum. The duct gives off a diverticulum which expands 

 into a rounded sac, the gall-bladder ; this acts as a recep- 

 tacle for the bile when it is not required. The bile has an 

 important action on the fatty matters of the food, converting 

 them into an emulsion and decomposing a small proportion 

 into glycerine and fatty acid. In addition to secreting the 

 bile the liver has another function to perform : it acts as 

 a storehouse for surplus carbohydrates absorbed from the 

 food. The carbohydrates — compounds of the nature of 

 starch and sugar — are converted in the liver into a sub- 

 stance known as glycogen or animal starch, which becomes 

 stored up in the cells to be given out again to the blood as 

 it is required for nutrition during the intervals of fasting ; 

 this function of the liver is known as the glycogenic function. 

 The pancreas, which is a much smaller gland than the 

 liver, produces a secretion, the pancreatic juice, which has 

 the effect of converting starch into sugar, proteids into 

 soluble modifications known as peptones, and of assisting in 

 the emulsification of fats. The duct of the pancreas also 

 opens into the duodenum. The nutrient matters of the 

 food, rendered soluble by the action of the various digestive 

 fluids, pass into the blood contained in the blood-vessels in 

 the wall of the enteric canal, and are thus conveyed through- 

 out the body to be distributed. The fatty matters, however, 

 pass into a system of minute vessels — the lac teals — which 

 ramify in the wall of the intestine. The lacteals are not 

 blood-vessels, but belong to the lymphatic vascular system to 

 be referred to presently. The lacteals combine together 

 and in the rabbit open into a large trunk — ■ the thoracic duct 

 — by means of which the absorbed emulsion, or chyle as it is 

 termed, is conveyed to one of the great veins. 



