760 PHYSIOLOGY 



found that the ammonium carbonate had disappeared and that its place was 

 taken by urea. If the liver is necessary for this conversion to take place and 

 ammonia is a constant precursor of urea, we should expect to find that the 

 abolition of the hepatic functions would cause the appearance in the urine 

 of ammonium carbonate or carbamate in the place of urea. The cutting out 

 of the liver is not, however, an easy matter in mammals. Ligature of the 

 portal vein, which would be a necessary step in the extirpation of the liver, 

 causes the blood to be dammed up behind the ligature in the portal area. 

 The intestinal wall gets full of effused blood, the blood pressure falls steadily, 

 and the animal dies within a few hours, being bled to death, so to speak, into 

 its portal vessels. A way of obviating this difficulty was suggested by a 

 Russian surgeon, Eck, and was successfully carried out by Pawlow. Before 

 ligature of the portal vein, this vessel was joined to the vena cava and an 

 artificial opening made connecting the lumen of the two vessels, so that, 

 after the ligature, the blood could flow directly into the general circulation 

 without passing through the liver. Some animals operated on in this way 

 showed no abnormal symptoms whatsoever. There was a rapid formation 

 of a collateral circulation so that the blood could get round the ligature to 

 the liver. Under all circumstances a path to the liver was still open by the 

 hepatic artery, but to arrive here the blood from the alimentary canal had 

 first to pass through the general circulation. A certain number of animals 

 were found to be particularly susceptible to the nature of their diet. On a 

 diet largely consisting of carbohydrates they maintained good health. After 

 a large meat meal, however, they became ill, and in many cases suffered from 

 tremors and convulsions ending in coma. At the same time there was a defi- 

 nite increase of ammonia in the urine, chiefly in the form of ammonium 

 carbamate. Analysis of the blood from a normal animal showed that 

 during protein digestion there was a constant excess of ammonia in the 

 blood of the portal vein above that in any other part of the vascular system. 

 In the carotid blood the normal amount, according to Nencki, is about 

 2 mg. per 100 c.c., in the portal blood 4 to 6 mg.* During the morbid 

 symptoms brought on by a protein meal in the animals in whom an Eck 

 fistula had been produced, the ammonia in the carotid blood may rise to as 

 much as 4 mg., i.e. to the amount normally found in portal blood. Pawlow 

 and Nencki therefore ascribed the symptoms observed in these dogs after 

 a heavy meat meal to a condition of ' ammonisemia,' and regarded the liver 

 as an organ which is normally concerned in protecting the rest of the body 

 from ammonia produced in the alimentary tract by converting this substance 

 into the innocuous neutral body, urea. 



This view of the function of the liver is confirmed by Schroder's experi- 

 ments on birds. In these animals the chief nitrogenous excretion is not urea, 

 but ammonium urate, 60 per cent, of the nitrogen of the urine appearing in 

 the form of uric acid. In birds there is naturally a communication between 

 the portal system and the general venous system by means of the vein of 



* According to Folin this excess of ammonia in the portal blood, when present, 

 is due to bacterial fermentation processes occurring within the intestine. 



