B UILDING- UP AND BREAKING-DO WN BODYSTUFFS. 893 



It is produced when these two substances are allowed to act upon one 

 another at a high temperature, and under pressure, as when they are 

 heated together for some hours in a glass tube to a temperature of 160 

 C., or more simply by heating monochloracetic acid with benzamide : 



C 6 H 5 CO.NH 2 +CH 2 C1.COOH=(C G H 5 CO)NH.CH 2 .COOH+HC1 



(benzamide) (monochloracetic acid) (hippuric acid) 



This synthesis of hippuric acid in vitro was speedily followed by that of 

 urea (Wohler, 1828). 



The synthesis of hippuric acid was proved by Bunge and Schmiede- 

 berg to occur in dogs exclusively in the kidney, and may be produced 

 even at the temperature of the room, by passing oxygenated blood 

 containing benzole acid, or a benzoate, and glycine through the blood 

 vessels of the organ, or even by allowing such blood to stand for a 

 while in contact with the minced kidney of a fresh-killed animal. 

 When, however, the kidney cells are destroyed, as by being pounded with 

 sand in a mortar, no hippuric acid is produced. If benzole acid be 

 given by the mouth, hippuric acid appears in the urine ; the glycine for 

 the synthesis is furnished by the tissues. If the kidneys are previously 

 extirpated, no hippuric acid is found in any % of the organs after the 

 exhibition of benzole acid; but if the ureters are merely ligatured, 

 hippuric acid is found in abundance. 



In frogs and rabbits the synthesis of hippuric acid is not confined to the 

 kidneys, but is found to occur after the extirpation of these organs. 1 



Other syntheses besides that of hippuric acid, which are known to 

 occur in the animal body, are that of urea in the liver, from ammonium 

 carbonate and ammonium carbamate ; that of uric acid in the bird's liver, 

 also from ammonia compounds ; that of glycogen, from glucose in the 

 liver, and also in muscles and in many other tissues ; that of proteids, 

 from peptones in the mucous membrane of the alimentary canal ; that of 

 fats, from fatty acids and glycerin in the intestinal mucous membrane ; 

 that of fats from carbohydrates, or from the elements of the broken-down 

 carbohydrate molecule ; and also, in all probability, that of fats from the 

 non-nitrogenous moiety of the broken-down proteid molecule. It is clear 

 from these instances that the importance of syntheses in the animal 

 economy cannot be overrated, and although the most striking feature in 

 animal metabolism is the breaking down of complex substances into 

 others of more simple form, yet even in the case of these broken-down 

 products there is frequently a subsequent synthesis before they are got 

 rid of from the body. Instances of this occur in the case of several urinary 

 products, such as hippuric acid, urea, and uric acid. 2 



As Bunge 3 remarks : " There are two reasons why these synthetic 

 processes in the animal body have excited the interest of physio- 

 logists and chemists. In the first place, they were in contradiction 

 to the long dominant doctrine of Liebig, as to the contrast be- 

 tween the metabolic processes in plants and animals; 4 and, in the 



1 Bunge and Schmiedeberg, Arch,, f. exper. Path. u. Pharmakol., Leipzig, 1876, Bd. vi. 

 S. 233 ; Hoffman, ibid., 1877, Bd. vii. S. 239 ; Kochs, Arch. f. d. ges. PhysioL, Bonn. 1879, 

 Bd. xx. S. 64 ; Salomon., Ztsclir. f. physiol. Chem., Strassbnrg, Bd. iii. S. 365. 



2 On the importance of synthetic processes in animal metabolism, see Pfliiger, Arch. f. d. 

 ges. PhysioL, Bonn, 1888, Bd. xlii. S. 144. 3 "Lehrbuch," 1894, S. 288. 



4 Nevertheless, the main distinction propounded by Liebig, that most plants are able 

 to obtain their nitrogen, and to build it up into proteid from inorganic materials, whereas 

 animals do not possess this power, still holds good. 



