776 SPECIAL PHYSIOLOGY. 



Daily quantity for 1 lb. weight of body substance, in a Man of 145 Ibs. 

 weight (Parkes). 



Water, 2.9 drachms. 



Urea, 3.53 grains. 



Uric acid, . .059 " 



Hippuric acid, . . . . . 



Creatin, 



Creatinin, 



Coloring matter, and other extractives, 

 Sulphuric acid, .... 

 Phosphoric acid, .... 

 Chlorine, 



.237 

 .032 

 .048 

 1.062 

 .214 

 .336 

 .875 



Composition of 100 parts of the Solid Constituents (Lehmann). 



Urea, 49.68 



Uric acid, 1.61 



Extractives: Creatin, Creatinin, Hippuric acid, Salts of ) QQ 95 

 Ammonia, Chloride of Sodium, j 



\ Alkaline sulphates, 11.58 



Alkaline phosphates, 5.96 



Phosphates of lime and magnesia, 1.97 



The water of the daily urine equals about one-half of that taken 

 into the stomach ; supposing the total quantity of the excretion to be 

 .from 30 to 50 oz., the water would be from 28 oz. to 47 oz. The 

 solid constituents amount to from 2 oz. to 3 oz. in the twenty-four 

 hours. 



The urea is by far the most important and characteristic substance, 

 amounting to upwards of an ounce, or half the solid constituents in 

 24 hours, or, according to some estimates, to as much as 500 grains. 

 Its atomic composition, CH 4 N 2 corresponds with that of carbamide, 

 COH 4 N 2 , and also with that of 1 atom of hydric cyanate of ammo- 

 nia, viz., CNOH-fNH 3 . It is readily transmutable, by the absorption 

 of the elements of two atoms of water, into carbonate of ammonia, 

 one atom of which contains C0 3 -J-2(NH 4 ). Urea is thus obtained: 

 Evaporate cautiously a considerable quantity of urine to the consis- 

 tence of syrup ; to this, add slowly its bulk of nitric acid, when cer- 

 tain crystals are thrown down, which are nitrate of urea ; dry these 

 upon a filter, decolorize them by dissolving them in water, and boiling 

 with animal charcoal, and recrystallize ; once more dissolve the crys- 

 tals and now separate the nitric acid, by means of carbonate of baryta. 

 On evaporating the solution, a pasty substance is left, from which 

 alcohol dissolves out the urea, and the filtered solution yields, on evapo- 

 ration, pure crystals of this substance. These crystals are long, col- 

 orless, four-sided prisms, extremely soluble in hot, and even in cold, 

 water ; hence urea never enters into the composition of urinary sedi- 

 ments or calculi. It dialyzes most actively. It is neutral in its reac- 

 tion to test paper ; but it acts as a base, combining with acids to form 

 definite salts. As hydric cyanate of ammonia is identical in composi- 

 tion, crystalline form, and chemical properties, with urea, and as the 

 former substance can be made in the laboratory, it affords an example 

 of the imitation of an organic compound, by artificial means. ( Wohler.) 

 Urea contains 46.7 per cent, of nitrogen, together with 20 per cent. 



