426 PHYSIOLOGICAL CHEMISTRY. 



treating cystin with tin and hydrochloric acid, only a little sulphu- 

 retted hydrogen is evolved and cystein is produced. On shaking a 

 solution of cystin in an excess of caustic soda with benzoyl-chloride 

 a voluminous precipitate of benzoyl-cystin is produced (BAUMANtf 

 and GOLDMANN). On heating on a platinum foil, cystin does not 

 melt hut ignites and burns with a bluish-green flame accompanied 

 by a peculiar sharp odor. 



Cystin is easily prepared from cystin calculi by dissolving them 

 in alkali carbonate, precipitating the solution with acetic acid, and 

 redissolving the precipitate in ammonia. The cystin crystallizes on 

 the spontaneous evaporation of the ammonia. The cystin dissolved 

 in the urine is detected, in the absence of albumin and sulphu- 

 retted hydrogen, by boiling with alkali and testing with lead salt or 

 sodium nitroprusside. To isolate cystin from the urine, acidify the 

 urine strongly with acetic acid. The precipitate containing cystin 

 is collected after 24 hours and digested with hydrochloric acid, 

 which dissolves the cystin and calcium oxalate, leaving the uric 

 acid undissolved. Filter, supersaturate the filtrate with ammonium 

 carbonate, and treat the precipitate with ammonia, which dissolves 

 the cystin and leaves the calcium oxalate. Filter again and pre- 

 cipitate with acetic acid. The precipitated cystin is identified by 

 the microscope and the above-mentioned reactions. Cystin as a 

 sediment is identified by the microscope. It must be purified by 

 dissolving in ammonia and precipitating with acetic acid and then 

 tested. Traces of dissolved cystin may be detected by the produc- 

 tion of benzoyl-cystin, according to BAUMANN and GOLDMANN. 



VII. Urinary Sediments and Calculi. 



Urinary sediment is the more or less abundant deposit which is 

 found in the urine after standing. This deposit may consist partly 

 of organized and partly of non-organized constituents. The first, 

 consisting of cells of various kinds, yeast-fungus, bacteria, sperma- 

 tozoa, casts, etc., must be investigated by means of the microscope, 

 and the following only applies to the non-organized deposits. 



As above mentioned (page 331), the urine of healthy individuals 

 may sometimes, even on voiding, be cloudy on account of the phos- 

 phates present, or become so after a little while because of the sepa- 

 ration of urates. As a rule, urine just voided is clear and after 

 cooling shows only a faint cloud (nubecula), which consists of 



