THE FINAL DESTRUCTION OF PROTEID 373 



during its passage through the kidneys of partially ridding itself of waste in 

 the form of uric acid. 



Allantoin appears in the urine of the dog after ingestion of uric acid 

 (Salkowski). It has been demonstrated also in the urine of man e.g., in 

 hepatic cirrhosis. This compound might, therefore, represent an intermediary 

 step in the destruction of uric acid. The genetic relationship -between the 

 substances considered here will be evident from the following formulae: 



HN CO HN CO NH 



II II / 



N C N ' HN C NIT NH-CII 



Hypoxanthin Uric acid Allantoin Urea 



(6-Oxypurin) (2, 6, 8-Trioxypurin) (Glyoxyl-diureid) (Carbamide) 



It appears from several observations that the liver is the seat of the destruc- 

 tion of uric acid. By artificial perfusion of this organ with blood, or by digestion 

 of uric acid with ground liver substance, uric acid disappears. Moreover, 

 according to Burian and Schur, it immediately appears in the blood of nephrec- 

 tomized dogs when the liver also is thrown out of the circulation. And yet 

 there are other observations which go to show that other organs also are capable 

 of decomposing uric acid. 



Uric acid therefore represents an intermediary product of metabolism in 

 Mammalia. In birds it is the chief nitrogenous end product of proteid, and is 

 formed for the most part by a synthetic process carried to completion in the 

 liver. A residue of urea and sarcolactic acid are probably to be regarded as the 

 basal material of this synthesis. 



The sulphur contained in proteid is eliminated in the urine mainly as 

 sulphates and ethereal sulphates ("acid sulphur"), but in part also as "neu- 

 tral sulphur" ( sulpho-cyanic acid, derivatives of taurin, cystein, oxyproteic 

 acid, and other organic compounds). A part of the sulphur moreover is 

 given off as taurocholic acid in the bile (cf. page 253). It is likely that this 

 sulphur comes mainly from the cystein group. 



As mentioned at page 127, it is very probable that under certain circum- 

 stances at least, carbohydrates are formed in the body from proteid, and, 

 indeed, that this may take place without the participation of the carbohydrate 

 group contained in most proteids. From all that we know of the manner 

 of cleavage of proteids, this formation of carbohydrates must be regarded 

 as a synthetic process, in which sugar is constructed by splitting off of the 

 amido groups, and by synthesis and partial oxidation of the N-free fraction 

 remaining (F. Miiller). 



According to a summary of Langstein, the following possibilities are to be 

 considered. Lactic acid can be obtained very easily from alanin by the action 

 of nitrous acid. This is an isomer of glycerin aldehyde which easily condenses 

 to dextrose. 



CH 3 OH, CH a .OH CH 2 .OH 

 CH.NH, CH.OH CH.OH (CH.OH) 4 

 COOH COOH CHO CHO 



Alanin Lactic acid Glycerin aldehyde Dextrose 



