CHAP. III.] 



TYROSINE. 



245 



jhat this organ contains an abundance of tyrosine as one of its 

 normal proximate principles. Ever since these researches were made 

 the error has from time to time been repeated and it cannot, there- 

 3, be too emphatically asserted that the pancreas during life con- 

 lins only a very small quantity of leucine and no tyrosine 1 . Both 

 these substances, as we have already stated, usually occur in large 

 quantities in -the dead pancreas, because of the rapid auto-digestion 

 )f the organ, a process which commences very shortly after death, 

 "t is only in the intestinal canal that tyrosine is a normal con- 

 tituent ; there it arises as one of the products of the action of trypsin 

 >n some portion of the hemipeptone which is the result of gastric 

 ind pancreatic proteolysis. 



Tyrosine occurs as a regular constituent in many invertebrate 

 mimals, especially in arthropoda. It was found by Warren de La 

 lue to be an abundant constituent of the cochineal insect (Coccus 

 iti). When thus found it is always associated with leucine. 



Tyrosine has been found (first by Frerichs), together with leucine, 

 in considerable quantities, in the Niiver, blood and urine of cases of 

 ;ute yellow atrophy and of acute phosphorus poisoning. In smaller 

 juautities, in cases of cirrhosis of the liver, and in the liver in severe 

 of typhoid fever and of small-pox. It has been found in puru- 

 lent sputa 2 , in the enlarged spleen in cases of leukaemia 3 , and has 

 Jen described as a constant constituent of the epidermal scales in 

 illagra 4 . 



Modes of Inasmuch as tyrosine is, with few exceptions, asso- 

 n of ciated in its origin with leucine, its modes of prepara- 

 tion have already been described, as well as the 

 methods which may be employed in separating it from leucine (see 

 pp. 234 and 236). It only remains therefore to note certain 

 exceptional cases in which by the decomposition of the albuminous 

 or albuminoid bodies, tyrosine is not obtained, and to give such 

 information as to the yield of tyrosine from various albuminous 

 and albuminoid bodies as was previously given in reference to 

 leucine. 



In general, whatever the proteid acted upon by such reagents as 

 dilute sulphuric acid, barium hydrate in aqueous solution at 150 

 160 C. &c., the products obtained are the same in kind; nevertheless 

 the amount of each product yielded by different substances may, 

 cceteris paribus, exhibit wide differences. Whichever the albuminous 

 or albuminoid body acted upon (with the single exception of the 



1 Kiihne, 'Erfahrungen und Bemerkungen iiber Enzyme und Fermente,' Unter- 

 suchungen aus dem Physiologischen Institute der Universitat Heidelberg, Vol. i. 

 p. 317. 



2 Fridreich, Virchow's Archiv, Vol. xxx. p. 381. 



3 Salomon, ' Zur Lehre von der Leukaemie,' Archiv f. Anat. u. Physiologic, 1876, 

 p. 762. Huber, ' Tyrosin und sein Vorkommen im thierischen Organismus,' Archiv 

 /. Heilkunde, Vol. xvin. (1877), p. 485. 



4 Schnitzer, quoted by v. Gorup-Besanez, Lehrbuch d. phys. Chem. p. 227. 



>sine. 



OF THE 



