ELEMENTS OF COMPOSITION. 



47 



volatile fatty acids (Frerichs and Staedeler) a change which certainly 

 takes place in the lower part of the intestinal canal. 



32. 



Tyrosin, C 9 H n N0 3 . 



This substance is also an amido-acid, whose constitution, however, has 

 not yet been fully ascertained. It possesses weak basic properties, and 

 may be obtained like the foregoing, but in much smaller amount, from 

 the artificial decomposition of protein matters. Not, however, like leucin, 

 from that of elastin and gelatin-yielding substances. It is also produced 

 by the putrefaction of protein compounds, and in especially large quan- 

 tity from the decomposition of silk-fibrin and glue. Keratin and animal 

 mucus also yield more tyrosin by far in their decomposition than the 

 original protein matters. Thus we see it to be associated chemically with 

 leucin, and it has been recently proved to be a physiological companion 

 of the same as a constituent both of the normal and diseased body 

 (Frerichs and Staedeler). Tyrosin, nevertheless, is not so extensively 

 met with as leucin. It crystallizes in white silky needles (fig. 29, a) 

 which are frequently arranged in very delicate, small, or large groups 

 (b b). While leucin is very soluble in water, tyrosin is but little so, 

 besides which it is insoluble in the pure state in alcohol and ether. It 

 fuses with decomposition when heated, and combines in regular propor- 

 tions with acids and bases. Warmed with concentrated sulphuric acid, 

 there is found in it, beside other acids, a compound named tyrosin-sulphuric 

 add, which, like its salts, when mixed with chloride of iron assumes a 

 beautiful violet colour (Piria's test). 



This reaction with chloride of iron just mentioned resembles that of 

 the salicylecompounds, although 

 its nature has not yet been as- 

 certained. 



Without taking into account 

 the tyrosin developed in the 

 processes of putrefaction in the 

 body, we find that it has similar 

 physiological sources to the fore- 

 going base. It is missed in the 

 healthy liver like leucin, pro- 

 bably because it undergoes there 

 rapid transformation into other 

 compounds. In disease, how- 

 ever, it appears in this organ. 

 Tyrosin which, as has been 

 already mentioned, springs in 

 smaller quantities from albu- 

 minous substances than leucin, 

 and lacks besides the physiologi- 

 cal sources of the latter from 

 gelatin and elastin, as well as its 



SOlubilitV, is frequently missed Fig. 29. Acicular crystals of tyrosin. a, single crystals 

 ' i . b b. smaller and larger groups of the same. 



where leucin occurs. 



Thus it has been found alone in no inconsiderable amount in the 



