680 THE SEAT OF FORMATION OF UREA 



in the ammonia of the portal blood from 1'3 mgr. per cent, 

 during starvation to 1'8 during the digestion of proteids might 

 be accounted for in this way ; but it is not the only possibility. 

 Horodynski, Salaski, and Zaleski found that the pancreas and 

 mucous membrane of the stomach and intestine contained a 

 higher percentage of ammonia, even during starvation, than any 

 other structure in the body. This percentage was greatly in- 

 creased during digestion and even during Pawlow's " sham- feed- 

 ing " experiments. This would seem to show that the tissue 

 metabolism of these digestive glands is marked by a considerable 

 production of ammonia. And it is striking that Vernon should 

 have found tissue erepsins more plentifully in the intestinal 

 mucous membrane, the pancreas and spleen, than in any other 

 tissue except the kidney. 



The importance of digestion in the alimentary canal as a 

 source of the precursors of urea is shown in some of Schroder's 

 experiments. He found that when the blood of a fasting animal 

 was circulated through its own liver, the urea content of the 

 blood was diminished by 5 per cent. If an ammonium salt was 

 then added to the blood and circulated through the liver for the 

 same length of time the urea content was increased by 153 

 per cent. When he circulated the blood of a well-fed dog in 

 digestion through its own liver he found that the urea content 

 of the blood was increased by 2 7 per cent, in the same time. 



The relative importance of the alimentary canal and the 

 other tissues of the body as sources of ammonia is shown by 

 the experiments of Hahn, Massen, Nencki, and Pawlow, and also 

 by those of Nencki, Pawlow, and Zaleski. They were performed 

 on dogs with a simple Eck's fistula. In this case the liver still 

 remains supplied by the hepatic artery, but the portal blood passes 

 direct into the inferior vena cava, and so into the general circula- 

 tion. Many of the dogs recovered completely from the operation 

 and lived for months without showing any symptoms of ill-health. 

 It was found, however, that when these dogs were fed on 

 meat or received glycin, salts of ammonium or carbamic acid 

 by the mouth, they rapidly became convulsed ; but that normal 

 dogs under the same circumstances showed no abnormal symptoms. 

 When the dogs were in convulsions, an examination of the blood 

 and urine showed that the ammonia content of the arterial blood 

 was raised very nearly to that of the portal vein, and that 



