THE MICROSCOPE IN MEDICINE AND SANITATION. 109 



of the white corpuscles will be treated somewhat more fully 

 in the next section; but their presence in urine is of 

 much significance since it is these cells which mainly 

 make up the whitish pus discharged from inflamed 

 surfaces. When the walls of the genito-urinary tract are 

 seriously affected, cells detached from its lining epi- 

 thelium will be noted in the urine. The appearance 

 of some of these elements is indicated in Fig. 42. 

 Finally, most renal diseases are characterized by the de-' 

 posit in the fine tubules of the kidney of an albuminous 

 substance which coagulates to form minute twisted tubes 

 (Fig. 43). These casts found in the urine may be clear 

 and hyaline or may be rendered granular by the presence 

 of disintegrated epithelial cells or may contain undecom- 

 posed epithelial cells or pus cells or fat globules or bacteria 

 according to the special pathologic condition from which 

 they arise. So-called waxy casts are denser and more 

 sharply marked than any other type and indicate an 

 advanced stage of renal disease. 



4. Examination of Blood. — ^The blood is a colorless 

 fluid or plasma containing cells of several distinct types 

 whose number and relative proportions vary in many 

 physiologic and pathologic states. Few clinical tests are 

 of more value to the physician both in diagnosis and 

 prognosis than the examination of this body fluid under 

 the microscope. 



For the study of the various types of cells the blood 

 must be dried and stained; and the preparation of a 

 good blood smear for staining is a matter of some deli- 

 cacy. The blood may be obtained from the lobe of 



