URINE 163 



liver, but evidence does not bear out this assumption. Probably 

 urea formation is a function of all cells of the body, but is par- 

 ticularly prominent in liver tissues. The liver cannot be removed 

 from the body of a mammal without causing the death of the ani- 

 mal in a few hours. The liver may be shunted out of the circu- 

 lation, however, by an operative procedure known as Eck's fis- 

 tula. In an Eck's fistula, the portal vein is joined to the inferior 

 vena cava. The portal vein beyond the fistula is then ligated. 

 The blood from the intestine now no longer passes to the liver, but 

 into the vena cava and thence to the heart. The liver still receives 

 some blood by way of the hepatic artery but most of the blood 

 does not pass through the liver. Under these circumstances, the 

 amount of urea decreases greatly, with a corresponding increase 

 in ammonia. It also has been observed that in various acute dis- 

 eases of the liver or in injury to the liver cells after poisoning 

 with certain substances, a fall in urinary urea results. This and 

 other evidence points to the conclusion that most of the urea is 

 formed in the liver, but that it also is formed elsewhere, perhaps 

 generally in the body. 



A small proportion of the urinary urea may arise from the 

 direct hydrolysis of one of the amino acid constituents of the pro- 

 teins, viz. arginine. Inspection of the formula for this compound 

 will demonstrate the ease of this process from a chemical stand- 

 point. There probably also are various other minor sources of 

 urea. 



Urea has a distinct physiologic action, acting as a diuretic. 

 Increase of urea in the blood increases the flow of urine. This 

 is in harmony with the fact that on high protein diet, the volume 

 of the urine also is high. 



Uric Acid and Other Purine Derivatives. Uric acid occurs 

 in the urine in amounts ranging from about 0.3 to 1.2 grams per 

 day. It makes up from 5-10% of the total nitrogen of the urine. 

 Notwithstanding its small amount, uric acid is of great interest, 

 and long has attracted widespread attention because it occurs as 

 a urinary sediment. On account of its insoluble character, it is 



