THE MICROSCOPE IN MEDICINE AND SANITATION. 107 



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 forrri 

 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 cofSn-shaped 

 crystals). (See Fig. 42.) In hyperemia, acute nephritis, 

 and some other conditions, red blood- corpuscles appear 

 in the urine as homogeneous, yelloAvish discs 7.5 ji 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 



