UKEA. 



395 



0*0063 grm. oxalic acid, we can easily calculate the amount of oxalic acid which is equivalent 

 to the degree of acidity in 100 c.c. of urine. So that the degree of acidity of the urine is 

 expressed by the equivalent amount of oxalic acid, which is completely neutralised by the 

 same amount of caustic soda. 



Urine of Mammals. The urine of carnivora is pale, passing into a golden-yellow ; its 

 specific gravity is high, and its reaction strongly acid. The urine of herbivora is alkaline ; it 

 shows a precipitate of earthy carbonates (hence, it effervesces on the addition of an acid), and 

 of basic earthy phosphates. During hunger, the urine presents the character of that of car- 

 nivora, as the animal in this case practically lives upon its own flesh and tissues. 



256. I. THE ORGANIC CONSTITUENTS OF URINE. Urea, C0(NH 2 ) 2 , 

 the diamide of C0 2 , or carbamid, is the chief end-product of the oxidation of the 

 nitrogenous constituents of the body. Its composi- 

 tion is comparatively simple : 1 carbonic acid + 2 

 ammonia - 1 water. It crystallises in silky four- 

 sided prisms with oblique ends (rhombic system), 

 without water of crystallisation (fig. 252, 1), if it 

 crystallises rapidly it forms delicate white needles. 

 It has no action on litmus, is odourless, and has a 

 weak, bitter, cooling taste, like saltpetre ; is readily 

 soluble in water and alcohol, but insoluble in ether. 

 It is an isomer of ammonium cyanate, from which it 

 may be prepared by evaporation, whereby the atoms 

 rearrange themselves (Wohler, 1828). It can be 

 prepared artificially in many other ways. 



Decomposition. When heated above 120, it gives off 

 ammonia vapour, while a glassy mass of biuret and cyanic 

 acid is left. When urine undergoes the alkaline fermenta- 

 tion ( 263), or when urea is treated with strong mineral 

 acids, or boiled with the hydrates of the alkalies, or super- 

 heated with water (240 C), it takes up two molecules of 

 water and produces ammonium carbonate, thus 

 CO(NH 2 ) 2 + 2H 2 = CO(NH 4 0) 2 . 



When brought into relation with nitrous acid, it splits up 

 into water, C0 2 , and N. The two last decompositions are 

 made the basis of methods for the quantitative estimation of 

 urea ( 257). 



Quantity. In normal urine, urea occurs to the 

 extent of 2*5 to 3*2 per cent. An adult man ex- 

 cretes daily from 30 to 40 grms. [500 grains, or a 

 little over 1 oz.]; women less, children relatively 

 more ; owing to the relatively greater metabolism in 

 children, the unit weight of body produces 

 more urea than the unit weight of an adult, 

 in the proportion of 1*7 : 1. If the metabol- 

 ism of the body is in a condition of equi- 

 librium ( 236), the urea excreted contains 

 almost as much N as is taken in with the 

 nitrogenous constituents of the food. 



Variations in the Quantity. The amount 

 of urea increases when the amount of pro- 

 teids in the food is increased j and also when there is a more rapid breaking up 

 of the nitrogenous tissues of the body itself. As this breaking up is increased 

 by diminution of O, and by loss of blood, so these conditions also increase the 

 urea ( 41). It is also increased by drinking large draughts of water, by various 

 salts, by frequent urination, and by exposure to compressed air. In diabetic 

 persons, who eat very large quantities of food, it may exceed 100 grms. [over 3 



Fig. 251. 

 Graduated burette. 



