THE FUNCTIONS OF THE DIGESTIVE ORGANS. 517 



The part played by bile in the animal organism has been variously 

 estimated at different times. Some have even regarded it as an excre- 

 tion. According to this view, the bile serves merely to carry away the 

 by-products which are formed as a result of the activity of the cells. We 

 know that the liver plays an important part in the metabolism of the 

 animal organism. Important decompositions and syntheses are con- 

 stantly taking place in its cells. Its position between the blood-vessels 

 of the viscera and those of the rest of the body make it easy to recognize 

 its numerous important functions. We have spoken of the position it 

 occupies with regard to carbohydrate metabolism, and have seen that at 

 one time the liver cells construct glycogen from glucose molecules, while 

 at another time it decomposes the latter into its constituents. Many 

 discoveries indicate that the liver plays an important part in the trans- 

 formation of fats and proteins into carbohydrates. Even in the metab- 

 olism of albumin it assumes a central position. In it is effected the 

 formation of urea and of uric acid. The liver captures the ammonia set 

 free in the alimentary canal and in the intestines themselves in order to 

 make use of it in various ways, partly for the formation of urea, and partly 

 for the neutralization of acid. The liver also stores up many substances 

 injurious to the organism, or at least foreign to it. This is shown by the 

 large amount of iron which accumulates here when large quantities of 

 this element are taken into the system, and by the fact that many other 

 substances are found in it which are otherwise foreign to the organism. 

 The liver also effects the combination of many substances injurious to the 

 system with sulphuric acid and glucuronic acid. It is indeed possible 

 that in these processes, which by no means include the entire functions 

 of the liver, waste products are constantly being formed which the cells 

 of the liver no longer have any use for, and are consequently given up to 

 the outside. This idea is supported by the fact that certain substances 

 found in the bile are not indifferent to the organism. Thus we know that 



