PROTEIN METABOLISM 805 



ard 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 ali- 

 mentary 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 definite increase of ammonia in the urine, chiefly 

 in the form of ammonium carbamate. Pawlow and Nencki therefore 

 ascribed the symptoms observed in these dogs after a heavy meat meal 

 to a condition of ' ammoniaemia,' 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. 



We thus see that the urea, which appears in the urine so rapidly after 

 an ingestion of protein, does not signify a total disintegration of the protein 

 molecule, bat is merely the result of the throwing off of the nitrogenous 

 part of the protein molecule by a process of deamination. This deamination 

 may be a purely hydrolytic change or it may be associated with oxidation 

 or reduction. Deamination of alanine, for instance, by simple hydrolysis 

 would result in the formation of lactic acid (an oxy -fatty acid). 



CH, CH- 



I I 



CH.NH 2 + H 2 = NH 3 + CHOH 

 COOH COOH 



If the deamination were accompanied with oxidation, the corresponding 

 keto-fatty acid would be formed, thus 



CH 3 .CHNH 2 .COOH + = NH 3 + CH 3 CO.COOH 



Alanine Pyruvic acid 



If reduction took place at the same time, the result' would be the production 

 of a saturated fatty acid such as propionic acid. Knoop has shown that 

 all three cases may occur. The investigation of the stages in deamination, 

 and indeed in the disintegration of fatty derivatives generally, is rendered 

 difficult by the fact that all the intermediate products undergo furt hex- 

 change and leave the body in a state of complete oxidation as carbon dioxide 

 and water. If however an amino-acid group be administered as part 

 of an aromatic compound, i. e. forming a side-chain of the benzene ring, 

 it is protected from complete oxidation by the stability of this ring. The 

 oxidation of the fatty side-chain may proceed to a certain degree, so that 



