538 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



feeding benzoic acid or compounds which the body converts into benzoic acid. 

 In a similar manner phenaceturic acid is found in the urine from the grouping 

 together of glycocoll and phenyl aeetic acid. Glycocoll and urea are to be 

 obtained by the decomposition of uric acid through hydriodic acid. Glycocoll 

 form.- colorless crystals, soluble in water and having a sweet taste. 



Glycocoll in th< Body. — If glycocoll be fed it is absorbed, burned, and 

 appears as urea in the urine. The fact that dogs, whose bile never contains 

 glycocholic acid, nevertheless excrete hippuric acid after being fed with ben- 

 zoic acid, indicates that, glycocoll may be considered a normal nitrogenous 

 decomposition-product of proteid. Its easy cleavage from gelatin, a product 

 manufactured from proteid in the body, confirms this. Heteroalbumose pre- 

 pared from fibrin likewise yields glycocoll on decomposition. 1 Continual daily 

 feeding of sufficient benzoic acid to fasting or casein-fed rabbits produces a con- 

 stant excretion of hippuric acid in such a proportion to total urinary nitrogen 

 as to indicate that 3 to 4 per cent, of the proteid molecule may be split off 

 in metabolism as glycocoll. 2 Feeding gelatin will not increase the hippuric 

 acid excretion as compared with the total urinary nitrogen. So glycocoll 

 may be a cleavage product of both gelatin and proteid metabolism. 



Amido- Adds in (inn nil. — These acids, such as glycocoll. aspartic acid, glutamic acid, 

 leucin, and tyrosin are found as putrefactive products of albumin and gelatin. Tn these 

 acids the amido- group is very stable, and cannot be removed by boiling with KOH. Tliey 

 are all converted in the body into the amide of carbonic acid (urea). Amido- acids may in 

 general be synthetically formed by heating mono-halogen compounds of the fatty acids with 

 ammonia: 



CH 2 C1C00H -f XH 3 = CH 2 NH 2 COOH + HC1. 



Methyl Amido-acetic Acid, or Sarcosin, CII 5 .NH.CH 2 .COOH.— This is not found 

 in the body, but is derived from death), theobromin, and caffein by heating with barium 

 hydroxide. 



Propyl Compounds. 



Normal or Primary Propyl Alcohol, CH 3 CH 2 CH 2 OH. — This is one of 

 the higher alcohols formed in the fermentation of sugar, and on oxidation 

 yields propyl aldehyde and propionic acid. 



Propionic Acid, CH 3 < II.,( '( >( )II. — Combined with glycerin this forms the 

 simplest fat ; salts of this acid feel fatty to the touch. Propionic acid is a 

 product of the dry distillation of sugar, of the butyric-acid fermentation of 

 milk-sugar, and of the put refaction of proteid. It is said to be present in the 

 sweat, in the bile, and sometimes in the contents of the stomach. Like others 

 of the lower fatty acids, it may partially escape oxidation and appear in traces in 

 the urine (see p. 536). 



..^-Acetyl Propionic Acid, or Levulic Acid, CH 3 COCII 2 CH 2 COOH.— This is the next 

 higher homologue to aceto-acetic acid. It has been obtained only by boiling sugars, espe- 

 cially levulose, with acid and alkalies, and since Kossel and Neumann 3 found that it is 

 yielded by some aucleins tiny conclude that this indicates the presence of the carbo- 

 hydrate radical in these aucleins. 



1 Spiro: Zeitschrift fiir physiologisehe Chemie, 1S99, Bd. 28, S. 174. 



2 Parker ami Lusk : American Journal of Physiology, 1900, vol. iii. p. 472. 



3 Verhandlung der Berliner physiologischen Gesellscbaft, Arehivfur Physiologic, 1894, S. 536. 



