PRODUCTION OF LEUCINE AND TYROSINE. 1 1/ 



they have not been detected in the juice of flesh, a circumstance 

 which appears the less surprising, however, when we remember 

 that even urea itself, an undoubted product of muscular meta- 

 morphosis, has never been satisfactorily recognised in healthy 

 muscular tissue, probably on account of its rapid removal by the 

 circulation. 



(126.) Artificially, leucine and tyrosine may be produced not 

 only from flesh, but also from blood-albumin, white of egg, gluten, 

 casein or cheese, gelatin, chondrin, elastic tissue, horn, nails, fea- 

 thers, hair, hedgehog-spines, cockchafer- elytra, &c. &c., by one 

 or other of two well-known indirect processes of oxidation, which 

 consist respectively in boiling the above-named substances for 

 many hours with some mineral acid, and in fusing them gently 

 with caustic alkali. Now, these two apparently opposite processes 

 are the same in principle. In each case, the acid or alkali merely 

 enables the protein or gelatinoid substance to react with water 

 H 2 O, whereby one portion of it becomes oxidised into leucine, 

 tyrosine, &c., while another portion is hydrogenised into divers 

 products. The nature of this action is best exposed by consider- 

 ing the case of some tolerably simple well-characterised sub- 

 stance such, for instance, as benz-aldehyd, or essential oil of 

 bitter almonds. When this body is treated with caustic potash, 

 one-half of it becomes oxidised into benzoic acid, which appears 

 in the form of an alkaline benzoate, and the other half is hy- 

 drogenised into benzyl-alcohol, as I mentioned a few minutes 

 ago: 



Benz-aldehyd Water Benzoic acid Benzyl-alcohol 



aC 7 H 6 + H a O = C 7 H 6 O a + C 7 H 8 



When, however, a large excess of alkali is used, and the action 

 allowed to become more violent, the hydrogen does not enter 

 into any combination, but is simply liberated in the gaseous state, 

 thus : 



Benz-aldehyd Water Benzoic acid Hydrogen 



C 7 H 6 + H 3 = C 7 H 6 3 + H 8 



