ESTIMATION OF SOLIDS. 393 



mum, after copious draughts of water, may be 1002; while the maximum, after 

 profuse perspiration and great thirst, may be 1040. The mean specific gravity is 

 about 1020. In newly-born children, the specific gravity falls very considerably 

 during the first three days, which is due to the amount of food taken (Martin and 

 Ruge). [The specific gravity of the urine in infants is about 1003 to 1006.] A 

 healthy adult excretes about 70 grms. [2J oz.] daily of solids by the urine, or 

 about 1 grm. of solids per 1 kilo, of body-weight. 



The specific gravity is estimated by means of a urinometer (fig. 250), the urine being at the 

 temperature of 16 C. [The urinometer, when placed in distilled water, ought to float at the 

 mark or zero, which is conventionally spoken of as 1000. Place the urine to be tested in a 

 tall cylindrical glass, of such width that the urinometer, when placed in it, may float freely 

 and not touch the sides. Take care that no air-bubbles adhere to the instrument. When 

 reading off the mark on the stem, raise the vessel to the eye and bring the e}-e on a level with 

 the surface of the water, noting the number which corresponds to this. This rule is adopted, 

 because the water rises on the stem in virtue of capillarity. It is essential that a sample of the 

 mixed urine of the twenty-four hours be used for ascertaining the mean specific gravity.] 



Christison's Formula. To estimate the amount of solids in the urine. This may be done 

 approximately by means of the formula of Trapp or Haeser, or, as it is called in this country, 

 "Christison's formula," viz., "Multiply the two last figures of a specific gravity expressed in 

 four figures by 2 "33" {Christison and Haeser), or by 2 {Trapp), or 2*2 (Loebisch). This gives 

 the amount of solids in every 1000 parts. [Suppose a person passes 1200 c.c. urine in twenty- 

 four hours, and the specific gravity is 1022, then 



22 x 2 -33 = 51 -26 grms. in 1000 c. c. 

 To ascertain the amount in 1200 c.c. 



1000 : 1200 : : 51-26 : x = 51 ' 2 ^ 200 = 61 -51 grms.] 



Direct Estimation of Solids. Place 15 c.c. of urine in a capsule of known weight, and 

 evaporate it over a water-bath, afterwards completely dry the residue in an air-bath at 100 C, 

 and then cool it over concentrated sulphuric acid. During the process, a small amount of urea 

 is decomposed, so that the value obtained is slightly too small. Of course the specific gravity 

 varies with the amount of water in the urine. The most concentrated (highest specific gravity) 

 urine is the morning urine (Urina noctis), especially after being retained in the bladder, e.g., 

 in prolonged sleep a certain amount of water is absorbed, so that the urine becomes more con- 

 centrated. The most dilute urine is secreted after copious drinking (Urina potus). Under 

 pathological conditions, as in diabetes mellitus ( 175), the urine is, at the same time, very 

 copious (as much as 10,000 c.c), and very concentrated, while the specific gravity varies from 

 1030 to 1060, [due to the presence of a large amount of grape-sugar]. In fever the urine is 

 concentrated, and small in amount. In polyuria, due to certain nervous conditions, the urine 

 is very dilute and copious, while the specific gravity may be as low as 1001. 



3. The colour of the urine depends on the colouring-matters present in it, and 

 varies greatly, but the differences in colour are due chiefly to variations in the 

 amount of water. Normally it has a pale straw colour, but if it contains more 

 water than usual it has a very pale tint, and in certain cases (as in the sudden 

 polyuria occurring after an attack of hysteria) it may be as clear as water. Con- 

 centrated urine, as after meals, or the first urine passed in the morning, has a 

 darker colour ; it is a dark yellow or brownish-red ; while it is usually dark 

 coloured in fever. 



Fcetal urine, and also the urine first passed after birth, are as clear and colourless as water. 

 The admixture of various substances with the urine alters its colour. When mixed with blood, 

 according to the degree of decomposition of the haemoglobin, the urine is red or dark brownish- 

 red [more frequently it is smoky], especially if the blood comes from the kidneys and the urine is 

 acid. When mixed with bile pigments, it is of a deep yellowish-brown, with an intense yellow 

 froth ; senna taken internally makes it intensely red, rnubarb brownish -yellow, and carbolic 

 acid black. Urine undergoing the ammoniacal fermentation may present a dirty bluish appear- 

 ance owing to the formation of indigo. The colour of urine is estimated by Neubauer and 

 Vogel by means of an empirical "colour-scale." 



Urine, but especially ammoniacal urine, exhibits fluorescence, which disappears on the 

 addition of an acid, and reappears after the addition of an alkali. 



Normal urine, after standing for several hours, deposits a fine cloud of vesical mucus [like 

 delicate cotton wool]. The froth of normal urine is white, and disappears pretty rapidly, while 

 that on an albuminous urine persists much longer. The urine not unfrequently contains some 

 epithelial cells from the bladder and urethra. 



