Il8 ANIMAL CHEMISTRY LECTURE V. 



Now, in fusing the above-mentioned animal substances with 

 caustic alkali, a greater or less proportion of gaseous hydrogen 

 from the decomposed tissue-water is similarly liberated ; whereas, 

 in boiling them with mineral acids, the same hydrogen, instead 

 of being liberated, effects certain hitherto unexamined combina- 

 tions or reactions ; while, in both cases, the oxygen of the decom- 

 posed water effects the production of leucine and tyrosine. Here 

 are specimens of leucine and tyrosine obtained in this way by the 

 action of sulphuric acid on feathers, and here another fine speci- 

 men of tyrosine, extracted from cochineal, all kindly lent me by 

 Dr. Hugo Miiller. 



(127.) Thus the conclusion that nitrogenous tissue contains a 

 something related to the fatty group and a something related to 

 the aromatic group, suggested by the results of its direct oxida- 

 tion with peroxide of manganese or chromic acid, is confirmed by 

 the results of its indirect oxidation with acids and alkalies. 

 Among fatty compounds, we obtain, in the one case, caproic 

 acid, and, in the other, amido-caproic acid, or leucine; while 

 among aromatic compounds we obtain, in the one case, benzoic 

 acid, and, in the other, ethyl-amido-salicic acid, or tyrosine. 

 Now, let us consider the constitution and respective relationships 

 of these amidated bodies. 



Starting from our primary fatty acids, we may obtain the 

 following series of chlorine derivatives : 



Fatty Acids a-Derivatives 



C H a 0, Formic C H Cl O a Chloro-formic? 



C a H 4 0, Acetic C a H 3 Cl 0, Chlor-acetic 



C 3 H 6 O z Propionic C 3 H 5 Cl 0, Chloro-propionic 



C 4 H 8 O a Butyric C 4 H 7 Cl O z Ckloro-butyric 



C 5 H I0 O a Valeric C 5 H 9 Cl 0, Chloro-valeric 



C 6 H Ia O a Caproic C 6 HnCl O a Chloro-caproic 



Now, if in each of these derived acids we replace the residue 

 of hydrochloric acid, or Cl, by the residue of water, or HO, we 

 obtain a new series of acids ; whereas, if we replace it by the 

 residue of ammonia, orH 2 N, we obtain a series of amides, thus: 



