NUTRITIVE VALUES. 51 



The explanation of the oxidation of the various amido acids in the 

 body is now generally referred to the relative position and number 

 of carbon atoms in the side chains. Schotten, a Pohl, 6 and Knoop c 

 have investigated this point quite thoroughly. The extent to 

 which the administration of various amido acids will maintain the 

 nitrogen equilibrium was first investigated by Loewi, d who showed 

 that the end products of digestion which no longer gave the biuret 

 reaction are still able to replace the albumins destroyed during 

 metabolism. 



Abderhalden and Bergell e have shown that amido acids when 

 given in moderate amounts (glycocoll up to 5 grams; alanin, 3 grams; 

 leucin, 8 grams; phenylalanin, 3 grams) are completely destroyed in 

 the body. Stolte^ injected various amido preparations into a rabbit 

 and found an increased urea output in all cases. According to Mann 

 the first change which the amido acids undergo in the body is prob- 

 ably that of oxidation, oxy-acids being formed as occurs in plants 

 and in alcaptan-urea when tyrosin and phenylalanin are changed 

 into homogentisinic acid. It is an open question whether the carbon 

 chain, after the splitting off of the nitrogen which forms urea, breaks 

 up still further or whether it is utilized in the building up of other 

 nonnitrogenous substances, such as carbohydrates and fats. Wohl- 

 gemuth h by feeding rabbits with the inactive or racemised mono- 

 amido acids (such as tyrosin, leucin, aspartic acid, and glutaminic 

 acid) found that the inactive acids become dissociated during meta- 

 bolism in such a way that the component occurring normally in the 

 body is oxidized as far as it can be assimilated while the abnormal 

 component is excreted partly or completely in the urine. 



The occurrence of monoamido acids in the urine during normal 

 and pathological conditions has been studied by Abderhalden/' Ab- 

 derhalden and Bergell/' Ignatowski,* Abderhalden and Barker/ and 

 Erben. m Loewi and Neuberg n have studied the diamins of the urine. 

 Since the discovery of the enzym erepsin in the intestine the idea is 

 rather generally accepted that the proteid molecule is broken down 

 in part, at least to the ammonia stage, and the ammonia and other 

 groups are synthesized into the characteristic body protein through 

 the agency of the epithelial cells of the villi of the small intestine and 

 transported by the lympocytes through the blood stream to the 

 tissues, 



a Zts. physiol. Chem., 1883, 8 : 60. h Ber. d. chem. Ges., 1905, 38 : 2064. 



b Arch, exper. Path. Pharm., 1896, 37: 413. i Zts. physiol. Chem., 1903, 38 : 557. 



« Hofmeister's Beitrage, 1904, 6 : 150. 1 Ibid., 1903, 39 : 9, 464. 



d Arch, exper. Path. Pharm. , 1902, 48: 303. * Ibid. , 1904, tf : 371. 



« Zts. physiol. Chem., 1903, 39:9. I Ibid., 1904, 42 : 524. 



/ Hofmeister's Beitrage, 1903, 5:1b. m Ibid., 1904, 43 : 320. 



9 Chemistry of the Proteids, 1906. n Ibid., 1904, 43 : 355. 



