THE MICROSCOPE IN MEDICINE AND SANITATION. 1097 
3. The Examination of Urine ——Many organic diseases 
affect materially the composition of the urinary secretion. 
Its amount, reaction, and specific gravity are significant, 
and chemical tests for sugar, albumin, etc., are of much 
value. The presence of certain important organized 
elements is determined under the microscope. 
The precipitate which forms in any urine on standing 
must be first concentrated by sedimentation, or better, 
by the use of the centrifuge, transferred by a pipette to a 
clean slide, covered, and examined with the high power. 
The edges of the preparation, where evaporation is taking 
place, should be avoided, since the crystals which form 
here are not characteristic. 
The principal objects which may be found in an 
examination of urinary sediments are crystals of certain 
products of metabolism, red and white blood-cells, epi- 
thelial cells, and tube-casts. The inorganic salts precipi- 
tated may be diverse in character, including uric acid 
(clusters of rhombic prisms and whetstone forms), acid 
urates (amorphous, granular masses soluble on warm- 
ing), calcium oxalate (small octahedral crystals whose 
diagonal planes look like the edges on the back of an 
envelope), and ammonium-magnesium phosphate (long 
prisms with bevelled edges, known as the coffin-shaped 
crystals). (See Fig. 42.) In hyperemia, acute nephritis, 
and some other conditions, red blood-corpuscles appear 
in the urine as homogeneous, yellowish discs 7.5 » in 
diameter, sometimes distorted to a globular form or shriv- 
elled and crenated almost beyond recognition. An arbi- 
trary line is drawn between “normal” cells retaining 
