URINE. 519 



small culs-de-sac, in each of which lies a plexus of 

 capillary vessels. 



Chopped kidney substance, when ground in a mor- 

 tar, becomes almost liquid. If this is strained, a com- 

 paratively very small quantity of solid substance re- 

 mains behind, consisting of the membranes of the fine 

 bloodvessels and the tubuli uriniferi. The strained, 

 milky and mucous liquid coagulates when heated, 

 forming a gelatinous mass, which consists principally 

 of albumen. 



The watery extract of kidneys contains, further, in 

 small quantity xanthine, sarcine, iuosite, taurine, and 

 leucine. 



Normal human urine is acid, principally owing to 

 the presence of acid sodium phosphate ; it has an un- 

 pleasant saltish and bitter taste ; has a mean specific 

 gravity of 1.020 ; always deposits a cloudy layer of 

 mucus ; and after a time becomes more strongly acid, 

 microscopic crystals of uric acid and sometimes calcium 

 oxalate being thrown down. Later it again becomes 

 neutral, finally alkaline, commencing to undergo de- 

 composition and emitting a foul odor, the formation 

 of ammonium carbonate and crystals of magnesium 

 ammonio-phosphate taking place. 



In its ordinary condition urine contains between 

 7-8 per cent, of solid ingredients ; the rest is water. 

 This relative proportion is, however, exceedingly vary- 

 ing, according to the quantity of liquid taken into 

 the body as drink, according to the evaporation from 

 the skin and the condition of health. 



The characterizing ingredients of human urine are 

 urea (p. 227), and uric acid (p. 232). 



When urine is evaporated down to the consistence 

 of honey, and allowed to stand for a long time covered 

 up, crystals of urea or of a compound of it with so- 

 dium chloride are formed. If in this concentrated 

 condition it is mixed with an excess of nitric acid, it 

 forms a pulp of crystalline scales, which are urea ni- 

 trate. Normal human urine contains between 2.5 and 



