308 Biological Chemistry. 



usually, however, lead to any results of value, as the same 

 end products are formed as when the primary substance is 

 ingested. Thus, both proteins and their degradation pro- 

 ducts, such as peptones and amino-acids, when adminis- 

 tered to animals, give rise to the same nitrogenous end 

 products in the urine, the chief of which is urea. To 

 overcome difficulties of the character just described various 

 devices have been suggested. Thus, intermediary pro- 

 ducts have been administered to animals in quantities 

 larger than those which can be completely broken down 

 into the final end products. In this case it might be] 

 expected either that the substance administered would be j 

 excreted unchanged, or that some product intermediate 1 

 between it and its final degradation products would be -I 

 eliminated in the urine. When this method of investi- I 

 gation is adopted, the intermediary product under investi- 

 gation is often administered by intravenous, intraperitoneal, j 

 or subcutaneous injection instead of by the mouth. Two 

 examples of this method of experiment may be cited, j 

 When dextrose is given to rabbits in large quantities,] 

 appreciable amounts of oxalic acid are excreted in the*! 

 urine. This acid appears, therefore, to be an oxidation ! 

 product of the sugar which is produced in the organism, 

 but which, under normal circumstances, is oxidized further; 

 to carbon dioxide and water. Again, when xanthine isM 

 administered to dogs it gives rise to allantoin, which id 

 excreted in the urine. If, however, xanthine is given inl 

 large quantities, certain amounts of uric acid are alsoj 

 eliminated. It would appear, therefore, as if uric acid is 

 a product intermediate between the xanthine and the- 

 allantoin, which is produced normally by the oxidation 

 the base in the organism of the dog. The relationshi] 

 of these substances to one another is illustrated in tl 

 following formulae : 



