THE SEAT OF FORMATION OF UREA 681 



in the urine the percentage of the total nitrogen excreted as 

 urea was decreased, whilst the percentage present as ammonium 

 salts was increased sufficiently to render the urine alkaline. 

 Among other ammonium salts present was the carbamate. 

 From these results it was concluded that the convulsions were 

 due to poisoning by salts of ammonium or carbamic acid. On the 

 other hand these observers found that, if dogs with an Eck's 

 fistula were fed on a mixed diet containing but little proteid, 

 the ammonia content of the blood and urine might be normal 

 and no convulsions ensue. The explanation of the different 

 result in these two cases appears to be that the liver, when 

 supplied only by the hepatic artery, is capable of converting 

 into urea the ammonia slowly produced by the tissues generally, 

 but that when larger quantities of ammonia enter the portal vein 

 rapidly during digestion, and especially the digestion of proteids, 

 the liver does not receive this increased supply of ammonia 

 sufficiently quickly to prevent poisoning. From these experi- 

 ments we may draw the following conclusions : that the alimentary 

 canal is an important source of ammonia ; that the digestion 

 of proteids increases the ammonia content of the portal vein 

 more than the digestion of other food-stuffs ; and that the liver 

 is the chief, if not the only organ, which can convert ammonium 

 salts into urea. 



The overwhelming importance of the liver in this conversion 

 is shown by other experiments. The analyses . of Horodynski, 

 Salaskin, and Zaleski show that the liver is the only organ which 

 abstracts ammonium salts from the blood. Some experiments by 

 Schroder suggest that the liver alone is capable of carrying out 

 this conversion. He found that extirpation of the kidneys in 

 dogs leads to a slow accumulation of urea in the body, and that it 

 took twenty- seven hours for the urea content of the blood to be 

 increased by four and a half times. If after the nephrectomy 

 ammonium salts or a carbamate were injected into the animal, the 

 urea content of the blood might be increased 100 per cent, in an 

 hour. When, however, the liver was put out of circulation in 

 addition to the removal of the kidneys, the injection of ammonium 

 salts led to no increase of urea in the blood within the period of 

 the experiment, one and a half hours. 



We have already seen that there is conclusive evidence that 

 mono-amino acids given by the mouth are excreted chiefly as 



