250 A MANUAL OF VETERINARY PHYSIOLOGY 



rapidly wastes. This condition may be experimentally produced 

 in the dog by the removal of the pancreas, which renders the 

 animal diabetic ; and though we are anticipating matters, as this 

 question must again be considered in dealing with that organ, it 

 may here be stated that the removal of the pancreas produces 

 diabetes, for the reason that the internal secretion of that gland, 

 which is referred to above, activates a pro-ferment in the muscles, 

 by which means the sugar is oxidised. 



Further Uses of the Liver. 



We have studied two uses of the liver- — viz., the formation of 

 bile and the storing up of glycogen — but there are other functions 

 of this gland to consider. 



The Formation of Urea. — When the complex protein molecule 

 of the food is broken down into simpler end-products, one of 

 these, known as ' urea,' is excreted by means of the kidneys ; this 

 substance, however, is not formed in these organs. It is proved 

 conclusively that part, at least, of the urea in the body is formed 

 in the liver. During the process of protein disintegration certain 

 amino acids, known as leucine and tyrosine, are produced, either 

 in the intestinal canal under the influence of pancreatic digestion, 

 or in the living cell as the result of the breaking down of protein. 

 Under any circumstances the leucine undergoes a series of 

 oxidative changes mainly in the liver, which result in the for- 

 mation of urea. 



The further facts regarding the formation of urea are best 

 dealt with in the section devoted to the kidneys. 



As the result of protein decomposition in the intestinal canal 

 certain aromatic compounds are formed ; these are united with 

 sulphuric acid, and got rid of by the kidneys as conjugated 

 sulphuric acids. In this combination the originally poisonous 

 protein products are converted into non-poisonous ones, and this 

 change is effected in the liver (Bunge). In this we have a very 

 important function of the liver demonstrated — viz., as a neutral- 

 iser of poisons introduced into the blood by the intestines. It 

 is a noteworthy fact that many metallic poisons are also arrested 

 in the liver — for example, mercury and arsenic. 



The numerous and complicated changes produced by the liver 

 may thus be summarised : It forms bile, regulates the supply of 

 sugar to the system, and stores up as glycogen what is not 

 required. It guards the systemic circulation against the intro- 

 duction of certain nitrogenous poisons, such as ammonia, by 

 transforming them into urea, and against other poisons of protein 

 origin by converting them into harmless products, by conjugation 

 with alkaline sulphates. 



