CONSTITUTION OF TYROSINE. 125 



C 2 H 3 (C H 3 .HN)0, Sarcosine, or methylamid-acetic acid 

 C 7 H 5 (C a H 5 .HN)0 3 Tyrosine, or ethylamid-salieic acid 



(133.) Lastly, Dessaignes having prepared hippuric acid by 

 substituting a residue of glycocine (C 2 H 3 O 2 .HN) for the atom of 

 chlorine in chlorobenzoic aldehyd C 7 H 5 (C1)O, the relationship of 

 hippuric acid and tyrosine to one another and to the benzoic and 

 psrsalicic acids may be shown by the following formulae, the par- 

 entheses of which are merely intended to point out the exchanged 

 portions of the original and derived bodies : 



Benzoic acid Hippuric acid 



C 7 H 5 (HO)0 C 7 H 5 (C 2 H 3 Z .HN)0 



Persalicic acid Tyrosine 



C 7 H 5 (HO)0 3 C 7 H 5 (C 2 H 5 .HN)0 3 



Now, ethylamine is indirectly convertible into glycocine by 

 oxidation, whereas salicic acid is convertible into benzoic acid 

 by deoxidation; or the fatty 2-carbon constituent of hippuric 

 acid is more highly oxidised, whilst its aromatic /-carbon con- 

 stituent is less highly oxidised than are the corresponding residues 

 of tyrosine.* Doubtless, therefore, the natural production of the 

 two bodies by tissue metamorphosis takes place under diiferent 

 conditions. Their joint occurrence in the urine, however, together 

 with that of indigo and phenol, confirms the inference we have 

 already drawn that be the chemical constitution of nitrogenous 

 tissue what it may, there exist 'in its molecule one or more group- 

 ings belonging to the fatty family, and yielding fatty oxidation- 

 products, together with one or more groupings belonging to the 

 aromatic family, and yielding aromatic oxidation-products. In my 

 next lecture we shall consider the intimate constitution of uric 

 acid and its congeners. 



* Since this lecture was delivered, Earth has rendered it probable that 

 the aromatic constituent of tyrosine is not ordinary salicic acid, but the 

 particular variety or isomer of it, which is known as paroxibenzoic acid. 



