236 THE MICROSCOPIST. 



Dr. Bird has also given another table, from which it 

 appears that the figures of specific gravity will indicate 

 nearly the amount of solids in each fluid ounce. Thus, 

 specific gravity 1010 shows a little more than 10 grains 

 of solids to the ounce ; 1020 equals a little over 20 grains ; 

 above 1030 a grain or two more must be added, as 1030 

 equals 31 J grains ; 1035 gives about 37 grains. 



The proportion of urinary excretion to the weight of 

 the body is often an important consideration. It may be 

 stated, as an average, to consist of about 149 grains of 

 water and 6J grains of solids to each pound weight in 

 twenty-four hours. 



The tables given by different observers vary, but the 

 above may serve as an average approximation. 



Urea is the vehicle by which nearly all the nitrogen of 

 the exhausted tissues is removed from the system, and its 

 retention is often attended with fatal ursemic poisoning of 

 the blood. In health, 400 to 500 grains are excreted in 

 twenty-four hours, but in some cases of kidney diseases 

 not more than 100 grains are eliminated, while in some 

 fevers over 1000 grains are removed in the same period. 

 If urea be suspected in excess, a drop of urine added to a 

 drop of nitric acid may be placed under the microscope, 

 when the characteristic crystals of nitrate of urea will 

 appear (Plate XXVI, Fig. 192). 



Volumetric analysis is the best means of ascertaining 

 the quantity of urea, as of other chemical ingredients, but 

 the practitioner may approximately estimate by weighing 

 the crystals of nitrate of urea formed by adding nitric 

 acid to double the quantity of urine, which has been con- 

 centrated to half its bulk by boiling. 



The proportion of uric acid varies from 0.3 to 1 part in 

 1000 of healthy urine. It may be obtained by adding a 

 few drops of hydrochloric acid to urine concentrated to 

 half its bulk, and allowing it to stand in a cool place. 



The estimation of the chlorides in urine is sometimes 



