364 HANDBOOK OF PHYSIOLOGY. 



variation may be greater; sometimes descending, in albuminuria, to 

 1004, and frequently ascending in diabetes, when the urine is loaded 

 with sugar, to 1050, or even to 1060. 



Quantity. The total quantity of urine passed in twenty-four hours 

 is affected by numerous circumstances. On taking the mean of many 

 observations by several experimenters, the average quantity voided in 

 twenty-four hours by healthy male adults from 20 to 40 years of age has 

 been found to amount to about 52J fluid ounces (H to 2 litres). 



Abnormal Constituents. In disease, or after the ingestion of special 

 foods, various abnormal substances occur in urine, of which the follow- 

 ing maybe mentioned Serum-albumin, Globulin, Ferments (appar- 

 ently present in health also), Peptone, Blood, Sugar, Bile acids and 

 pigments, Casts, Fats, various Salts taken as medicine, Micro-or- 

 ganisms of various kinds, and other matters. 



The Solids of the Urine. 



(1.) Urea. (CH 4 N 3 0.) Urea is the principal solid constituent of 

 the urine, forming nearly one-half of the whole quantity of solid matter. 

 It is also the most important ingredient, since it is the chief substance 



FIG. 251. Crystals of Urea. 



by which the nitrogen of decomposed tissue and of any superfluous food 

 is excreted from the body. For its removal, the secretion of urine seems 

 especially provided; and by its retention in the blood the most pernicious 

 effects are produced. 



Properties. Urea, like the other solid constituents of the urine, ex- 

 ists in a state of solution. When in the solid state, it appears in the 

 form of delicate silvery acicular crystals, which, under the microscope, 

 appear as four-sided prisms (Fig. 251). It may be obtained in this state 

 by evaporating urine carefully to the consistence of honey, acting on the 

 inspissated mass with four parts of alcohol, then evaporating the alco- 

 holic solution to dryness, and purifying the residue by repeated solution 

 in water or in alcohol, and finally allowing it to crystallize. It readily 



