SOURCE OF UREA. 155 



ured gives the volume of nitrogen set free. The glass 

 tubes (D, etc.) should be of small diameter. If there is 

 no leak in the apparatus, pressing the stopper into the 

 bottle A will force water from B into the tube D, and it 

 should remain full, without running out, as long as the 

 apparatus is not disturbed. 



Urea is probably formed in the liver. Its source is 

 the nitrogenous compounds of the food and the tissues, 

 including the blood, most of the nitrogen of such com- 

 pounds being excreted from the body in the urea. Hence 

 any increase in the destruction of these substances is ac- 

 companied by an increased formation of urea and vice 

 versa. For this reason the urea is considered as a measure 

 of the decomposition of the proteins in the body. 



Some things which bring about an increased decom- 

 position of proteins are: a large amount of nitrogenous 

 food, like meat; excessive exercise, which causes a de- 

 struction of tissue, though here the urea is not propor- 

 tional to the exertion; fevers and inflammations up to the 

 crisis, owing to the rapid loss of muscular tissue. After 

 the crisis it is diminished. In phosphorus poisoning and 

 diabetes mellitus the urea is excessive for the same reason. 

 A greater excretion of water, either from excessive drink- 

 ing or diuretics, carries with it a larger amount of urea, 

 which seems to be thus washed out of the system. 



On the .other hand, less urea is excreted during hunger 

 and sleep, when the metabolism of the body is lessened. 

 Interference with the excretory power of the kidneys like- 

 wise diminishes the urea. This is seen in acute nephritis 

 and other diseases of the kidneys. In such cases the pro- 

 duction of urea is not stopped, but it accumulates in the 

 system, often being accompanied by urasmic poisoning. 

 Since the urea is formed, at least in part, in the liver, we 



