APPENDIX. 831 



urates, and never free unless under abnormal conditions. A deposit of 

 urates may occur when the urine is concentrated or extremely acid, and 

 in febrile disorders. 



Xanthin or Di-oxypurin, C 5 H 4 N. O 2 , has been obtained from the 

 liver, spleen, thymus, muscle, and the blood. It is found in normal 

 urine, and is a constituent of certain rare urinary calculi. 



Hypoxanthin or Oxypurin, C 5 H 4 N 4 0, is found in juice of flesh, in 

 the spleen, thyrnus, and thyroid. 



Guanin or Amino-oxypurin, C 5 H 5 N 5 0, has been found in the human 

 liver, spleen, and fseces, but does not occur as a constant product. 



Adenm or Amino-purin, C 5 H a N 5 , is the simplest member of the 

 purin group. It exists abundantly in the liver and urine of leucocy- 

 themic patients. 



AUantoin, C 4 H 6 N 4 O 3 , found in the allantoic fluid of the foetus, and 

 in the urine of animals for a short period after their birth. It is one of 

 the oxidation products of uric ayid, which on oxidation gives urea. 



In addition to the above compounds and probably related to them, are 

 certain coloring and excrementitious matters, which are also most likely 

 distinct decomposition compounds. 



Pigments, Etc. 



Bilirubin, 16 H 18 N 2 3 , is the best known of the bile pigments. It 

 is best made by extracting inspissated bile or gall stones with water 

 (which dissolves the salts, etc.), then with alcohol, which takes out cho- 

 lesterin, fatty and biliary acids. Hydrochloric acid is then added, which 

 decomposes the lime salt of bilirubin and removes the lime After ex- 

 tracting with alcohol and ether, the residue is dried and finally extracted 

 with chloroform. It crystallizes of a bluish-red color. It is allied in 

 composition to hsematin, as has been described. 



Biliverdin, C ]6 H J8 IST 2 4 , is made by passing a current of air through 

 an alkaline solution of bilirubin, and by precipitation with hydro- 

 chloric acid. It is a green pigment which is an oxidation product of 

 bilirubin. 



Bilifuscin, C 9 H n N0 3 , is made by treating gall stones with ether, 

 then with dilute acid, and extracting with absolute alcohol. It is a 

 non-crystallizable brown pigment. 



Biliprasin is a pigment of a green color, which can be obtained from 

 gall stones, and from bile which has been allowed to decompose. 



Bilihumin (Staedeler) is a dark brown earthy-looking substance, of 

 which the formula is unknown. 



Urochrome and Urobilin occur in bile and in urine ; the latter is prob- 



