78 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



water-bath until the ammonia has disappeared; on cooling 

 the tyrosine separates as a chalky mass; this is filtered off, 

 washed, and dried on filter-paper. 



Tyrosine, C 9 H U N0 2 , p-oxyphenyl a-amino-propionic acid, 



C 6 H 4 < QJJ QJJ/NJJ )COOH (4) * s a constant c l ea vage product 

 of albumin and horn substance (but not of gelatin or of tissues 

 which may be converted into gelatin), formed by the action 

 of dilute acids or alkalies and also on putrefaction. It forms 

 shining silky needles, melting at 310-314 with decomposi- 

 tion. It is very difficultly soluble in cold water, slightly in 

 hot water, insoluble in alcohol and ether, soluble in ammonia 

 and caustic alkalies. 



Reactions of Tyrosine. 



(a) Heat a small portion in a test-tube with some water 

 to boiling, let cool slowly (without cooling in water), and 

 examine the crystals under the microscope : tufts of needles, 

 usually of very regular form, which readily dissolve on the 

 addition of hydrochloric acid and do not melt when warmed 

 gently on the slide of the microscope (distinction from the 

 needles of fatty acids in old pus, etc., which often resemble 

 tyrosine needles, and from the needles of fat, which form oily 

 drops on warming and do not dissolve in hydrochloric acid). 



(b) Suspend a small quantity of tyrosine in water in a test- 

 tube, add a few drops of Millon's reagent and heat gently till 

 boiling begins. The mixture at first turns rose-red, then 

 gradually deep red, frequently, however, not till it has stood 

 some time ; if the quantity of the tyrosine is somewhat large, 

 the solution becomes cloudy and gradually deposits a red 

 precipitate. Strong boiling is not advisable, as the reaction 

 is then often not so good and the color is more brownish. All 

 benzene derivatives in which a hydrogen atom of the benzene 

 nucleus is replaced by a hydroxyl group give the same reaction. 



