242 LECTURE XL 



diet of albuminous material, but that this also occurs after the addition 

 of the free amino acids, glycocoll and alanine. It is very significant that 

 the administration of ammonium carbonate is followed by a sharp decline 

 in the formation of ammonia, so that the ratio of ammonia-nitrogen to 

 the total nitrogen in the urine becomes less than under normal conditions. 

 We cannot conceive that the amino acids mentioned are capable of pro- 

 ducing acidosis on their own account, although we can imagine that 

 Siegfried's discovery, that the amino acids take on carbon dioxide forming 

 carbamic acids, is here expressed. On the other hand, this intermediate 

 acidosis gives us. an indication of the manner in which the decomposition of 

 the albumin cleavage-products is carried out in the tissues. It does not 

 seem improbable that acids are temporarily formed after the ammonia 

 has been split off, which cause an increase in the production of ammonia. 

 Our knowledge of the intermediate metabolism of albumin is so slight 

 at present that we have hardly any conception of these relations. 



We will now consider the end-products of albumin metabolism, which 

 occupy a different position from those just mentioned in that they are 

 not derived from the albumin cleavage-products as a whole, but can be 

 traced to definite amino acids. Among these is hippuric acid. It was 

 discovered in horse urine by Liebig. Its method of formation was known 

 to Keller and Wohler. 1 These authors noticed that when benzoic acid 

 was administered per os, it did not reappear as such in the urine, nor 

 could cleavage-products be found which were related to it. Keller and 

 Wohler, however, noticed an appreciable increase in the amount of hip- 

 puric acid. Its manner of formation is evident from its constitution. It 

 is broken down on boiling with strong mineral acids or alkalies, with the 

 addition of water, into benzoic acid and glycocoll: 



C 6 H 5 .CO.NH.CH 2 .COOH + H 2 O = C 6 H 5 .COOH + NH 2 .CH 2 .COOH 

 Hippuric acid Benzoic acid Glycocoll 



It may be synthetically produced from benzamide and monochlor- 

 acetic acid: 



C 6 H 5 .CONH 2 + C1.CH 2 .COOH = C 6 H 5 .CO.NH.CH 2 .COOH + HC1 



Benzamide Monochloracetic Hippuric acid 



acid 



It may also be obtained by heating glycocoll with benzoic acid in a 

 sealed tube for 1 or 2 hours at 160 degrees. 



The observation of Keller and Wohler, that benzoic acid appears in the 

 urine united to glycocoll, has been confirmed by numerous investigations 



1 Ann. 43, 108 (1842); Wohler and Frerichs; 66, 335 (1848); Wilhelm Wiechowski; 

 Hofmeister's Beit. 7, 204 (1905). 



