CHEMICAL BASIS OF THE ANIMAL BODY. 1275 



Tyrosine crystallizes in exceedingly fine needles which are 

 usually collected into feathery masses. The crystals are snow- 

 white, tasteless and odourless. If crystallized from an alkaline 

 solution tyrosine often assumes the form of rosettes composed of 

 fine needles arranged radiately. 



Fig. 226. Tyrosine Crystals. (Krukenberg.) 



The crystals are very sparingly soluble in cold water (1 in 

 2000 at 20°), much more soluble in boiling water (1 in 150); 

 they are almost insoluble in strong alcohol (1 in 13,500) and 

 quite insoluble in ether. They are readily soluble in acids 

 and particularly so in ammonia and other alkalis and in solu- 

 tions of alkaline salts. 



Preparation, (i) The products of a prolonged pancreatic 

 digestion of proteids are neutralized and filtered; the filtrate 

 when concentrated usually yields crusts of tyrosine crystals, 

 which may be readily purified by solution in a little boiling 

 water from which they separate out on cooling after concentra- 

 tion if necessary, (ii) Horn shavings are boiled for 24 hours 

 with sulphuric acid (5 of acid to 13 of water). The sulphuric 

 acid is then separated by the addition of lime, and the filtrate 

 from the calcium sulphate yields as before crusts of tyrosine 

 crystals on concentration and cooling. These are then purified 

 by recrystallization from boiling water. Any leucine at first 

 present in the crystalline crusts remains in the mother-liquors 

 from which the tyrosine has been separated. 



Apart from its crystalline form and characteristic solubili- 

 ties tyrosine may be readily recognized by several well-marked 

 reactions. 



Hoffmann's reaction. When heated with Millon's reagent, 

 solutions of tyrosine yield a brilliant crimson or pink colora- 

 tion which, if much tyrosine is present, is accompanied finally 

 by a similarly coloured precipitate. 



