I2O ANIMAL CHEMISTRY LECTURE V. 



been recognised in any natural or artificial product of animal 

 tissue. I am not aware that bulatine has yet been obtained 

 from any source whatever ; while phocine has been noticed upon 

 one occasion only by Gorup-Besanez in the pancreas of an ox. 

 Leucine, on the other hand, as I have already remarked, exists 

 naturally in, and is producible artificially from, a great variety of 

 animal and vegetable bodies. 



(129.) In commencing the study of the constitution of tyro- 

 sine, we are at once struck by the great resemblance which its 

 formula bears to that of hippuric acid. You observe that the 

 molecule of tyrosine differs in ultimate composition from the 

 molecule of hippuric acid, by an excess of two atoms of hydrogen, 

 thus : 



C 9 H 9 N 3 Hippuric acid 

 C 9 H U N 3 Tyrosine 



Inasmuch, however, as complex molecules of this description 

 are built up of the residues of several simpler molecules, it may 

 happen, and indeed not unfrequentlydoes happen, that the numbers 

 of the atoms of carbon, hydrogen, oxygen, and nitrogen in two or 

 more complex bodies, approximate very closely to, or are even 

 identical with, one another ; whilst the bodies themselves are com- 

 posed of very different residues, and accordingly have no real rela- 

 tionship of proximate constitution. Such, however, is not the 

 case with hippuric acid and tyrosine. Each of these bodies is 

 composed of three constituent residues namely, an ammonia 

 residue, a 2 -carbon residue belonging to the fatty, and a y-carbon 

 residue belonging to the aromatic class. That the aromatic resi- 

 due of tyrosine, however, differs from the residue of hippuric 

 acid in belonging to the salicic instead of the benzoic sub-group, 

 is evident from a variety of considerations pointed out by Schmitt 

 and Nasse, whose recently published views on the constitution of 

 tyrosine, if not demonstrated with absolute certainty, are so pro- 

 bable in themselves, and so supported by collateral testimony, as 

 to leave us in very little doubt as to their substantial correctness. 

 Thus tyrosine agrees with other salicic compounds in the charac- 

 teristic properties of yielding phenol by distillation, and chloranil 



