EPITHELIUM. 201 



nificance lias been explained before. It can be made more 

 visible by adding a little tincture of iodin, which colors it 

 brownish. The addition of acetic acid to the urine precipi- 

 tates nrncin as a fibrous mass. 



The epithelial cells, being continually thrown off 

 from mucous surfaces, are normally present in small num- 

 bers in the urine. In such cases they are usually from the 

 bladder and urethra, and, in women, from the vagina. A 

 large increase, however, is indicative of a diseased condi- 

 tion of some part of the urinary system. The cells from 

 different parts of the system are not all of the same shape. 

 (Plate III, 14.) They may be considered as belonging to 

 three classes: the squamous,, or pavement-epithelium; the 

 round celled; and the long, or spindle-celled, epithelium. 

 The squamous epithelium is composed of large, flat, some- 

 what irregular cells with a distinct nucleus. They may be 

 found singly or united, like the stones of a pavement. 

 They occur chiefly in the outer layers of the mucous mem- 

 brane of the vagina and bladder. The round-celled epi- 

 thelium has smaller cells with a nucleus and nucleolus 

 and are found especially in the tubules of the kidneys. 

 They are also found in the deeper layers of the mucous 

 membrane of other tissues, such as the bladder, urethra, 

 and pelvis of the kidney. They are somewhat larger than 

 the pus-corpuscles, and the nucleus can be seen without 

 clearing by acetic acid. The long-celled epithelium is nar- 

 row and somewhat irregular, with a nucleus visible with- 

 out staining. They are found in the outer layer of the 

 membrane of the renal pelvis or in the deep layers of the 

 bladder, ureters, and urethra. 



Although the presence of a single kind of epithelial 

 cells in the urine may give an indication of their origin, 

 still their occurrence in different tissues often renders this 



