6oo 
THE CHEMISTR Y OF THE URINE. 
progressive muscular atrophy, and in pseudo-hypertrophic paralysis. 
According to Senator, no increase is produced by the paroxysms of 
tetanus— a fact which is of interest as bearing on the relation of 
muscular activity to the urinary creatinin. 
(g) Hippuric acid. — Hippuric, acid is benzamido- acetic acid, or 
benzoylglycin, C 6 H 5 .CO.NH.CH 2 .COOH ; in other words, it is a con- 
densation' product of benzoic and amido-acetic acids, in the formation 
of which the hydroxyl group of the former is eliminated as water, 
with an atom of hydrogen from the amido group of the latter. But 
Fie 53. — A. Creatinin; B. Hippuric acid* 
the simplest artificial synthesis is obtained when monochlor-acetic acid 
is heated with benzamide. 
C 6 H 5 CO.NH 2 +CH 2 Cl.COOH = (C 6 H 5 .CO)NH.CH 2 .COOH+HCl 
In most mammals the synthesis by dehydrolysis occurs in the kidney ; 
hippuric acid appearing in the urine, whenever benzoic acid, or pre- 
cursors of benzoic acid, are taken by the mouth. The excretion of 
hippuric acid is, indeed, mainly dependent upon the relative richness of 
the diet in such precursors of benzoic acid. 
It is not necessary that benzoic acid should itself be ingested. A 
benzene derivative containing a single "side-chain" is nearly always 
oxidised in the body to benzoic acid. Such substances, therefore, as 
toluene, C 6 H 6 .CH 3 ; cinnamic acid, 6 H 5 .CH.OH.COOH ; or phenyl- 
propionic acid, C 6 H 6 .CH 2 .CH 2 .COOH, all give rise to an excretion of 
hippuric acid when they are taken by the mouth. Aromatic compounds 
of this type are abundantly present in some forms of vegetable food, as 
