142 BASIC BODIES. 



artificial conversion of one substance into the other,, the facts that 

 they occur in an inverse ratio in muscle and in urine, and that 

 putrid urine yields no creatine, but only creatinine, tend to show that 

 also, in the living body, the latter substance proceeds from the 

 former, and consequently is to be regarded purely as a product of 

 excretion. 



TYROSINE. C 16 H 9 NO 5 . 



Properties. This body forms silky, glistening, dazzlingly white 

 needles, is of very difficult solubility in water, and is altogether 

 insoluble in alcohol and ether; it dissolves readily in alkaline 

 solutions, and enters into combination with acids, with the excep- 

 tion of acetic acid. 



Composition. This body was discovered and analysed byLiebig.* 

 He regards, however, a repetition of the analysis as necessary for 

 the confirmation of the formula which he deduced. 



Preparation. Cheese, well pressed and freed from adherent 

 butter, or well-dried fibrin or albumen, must be fused, according to 

 Liebigand Boppt 5 with an equal weight ofhydrated potash, till, in 

 addition to ammonia, hydrogen begins to be developed, or, in other 

 words, till the original dark brown colour merges into a yellow ; on 

 then dissolving the mass in hot water, and slightly supersaturating 

 it with acetic acid, the tyrosine separates in needles, which are 

 obtained in a state of perfect purity by solution in potash-water 

 and a second acidulation with acetic acid. The adherent brownish 

 red pigment may be removed by treating the hydrochlorate of 

 tyrosine with animal charcoal, and boiling the colourless fluid with 

 an excess of acetate of potash ; chloride of potassium is then 

 formed, and the tyrosine, free from acetic acid, separates, on cooling, 

 in finely matted needles. This substance is also formed, together 

 with leucine and several acids of the first group, during the putre- 

 faction of albumen, fibrin, and casein. Finally, since tyrosine is 

 also formed in the decomposition of the above-named protein- 

 compounds by concentrated hydrochloric acid or by sulphuric acid, 

 (in which latter case leucine is also formed), this mode of procedure 

 may also be adopted for the preparation of this substance. For this 

 purpose we dissolve 1 part of the protein-compound in 4 times the 

 quantity of concentrated hydrochloric acid, and then add 4 parts of 



* Ann. d. Ch. u. Pharm. Bd. 57, S. 127. 

 t Ibid. Bd. 69, S. 19-37. 



