APPENDIX. 743 



Tyrosin, C 9 H U K"0 3 , is found generally together with leucin, in 

 certain glands, e. g., pancreas and spleen; and chiefly in the products of 

 pancreatic digestion or of the putrefaction of proteids. It is found in 

 the urine in some diseases of the liver, especially acute yellow atrophy. 

 It crystallizes in fine needles, which collect into feathery masses. It 

 gives the proteid test with Millon's reagent, and heated with strong 

 sulphuric acid, on the addition of ferric chloride gives a violet color. 



Lecithin, C 42 H 84 PN0 9 , is a complex nitrogenous fatty body, contain- 

 ing phosphorus, which has been found mixed with cerebrin and oleo- 

 phosphoric acid in the brain. It is also found in blood, bile and serous 

 fluids, and in larger quantities in nerves, pus, yelk of egg, semen, and 

 white blood-corpuscles. On boiling with acids it yields cholin, glycero- 

 phosphoric acid, palmic and oleic acids. 



Cerebrin, C 17 H 33 N0 3 , is found in nerves, pus corpuscles, and in the 

 brain. Its chemical constitution is not known. It is a light amorphous 

 powder, tasteless and odorless. Swells up like starch when boiled with 

 water, and is converted by acids into a saccharine substance and other 

 bodies. The so-called Protagon is a mixture of lecithin and cerebrin. 



UREA AND ITS ALLIES. 



Urea or Carbamide, CON 2 H 4 , is the last product of the oxidation 

 of the albuminous tissues of the body and of the albuminous foods. It 

 occurs as the chief nitrogenous constituent of the urine of man, about 2 

 to 3 per cent, and of some other animals. It has been found in the 

 blood and serous fluids, in lymph, and in the liver. 



Properties. Crystallizes in thin glittering needles, or in prisms with 

 pyramidal ends. Easily soluble in water and alcohol, insoluble in ether 

 It may be produced artificially by treating carbonyl chloride (COC1J with 



/OP TT 



ammonia; or by heating ethyl carbonate with ammonia CO^" Qn 2 TT 5 + 



2NH^ = CON" 2 H 4 2C 2 H 6 0; by heating carbonate of ammonium 

 CO 7 Q^Jj = CON 2 H 4 + H 2 0; by adding water to cyanamide CN.NH 2 , 



or by evaporating ammonium cyanate in aqueous solution. When heated 

 with water in a sealed tube to 100 C. or on allowing urine to stand, 

 urea splits up into carbonic acid and ammonia; when heated to a high 

 temperature urea loses ammonia and first yields biuret C 2 H 6 N~ 3 2 , and 

 after cyanuric acid, C 3 H 3 3 N 3 . It is decomposed by sodium hypochlo- 

 rite or hypobromite, or by nitrous acid with evolution of N". It forms 

 compounds with acids, of which the chief are urea hydrochloride CH 4 

 N 2 O.HC1; urea nitrate, CH 4 N a OHN0 8 ; and urea phosphate CH 4 JST 2 0. 

 H 3 P0 4 . It forms compounds with metals such as HgO.CH 4 N 2 0; with 

 silver CH 2 N 2 Ag 2 ; and with salts such as HgCl 2 . 



Urea is isomeric with ammonium cyanate C/-T from which it 



was first artificially prepared. 



Kreatin, C 4 H 9 N 3 2 , is one of the primary products of muscular dis- 



