BACTERIA. 205 



They do not seem to be characteristic of any pathological 

 condition of the kidneys, but rather of some irritation of 

 the lower urinary tract which has extended to the kidneys. 



All casts are decomposed by bacterial action. The 

 examination should, therefore, be made as soon as possible 

 after the urine is passed and the casts have settled. This 

 time may be shortened to five minutes by the use of the 

 centrifuge. Without this it will be necessary to let the 

 urine stand several hours or over night. 



420. To examine urine for casts a few drops from 

 the sediment obtained from standing in a conical glass 

 or from the centrifuge is placed upon the microscope- 

 slide; one with a shallow cell on top is best. Cover it 

 with a cover-glass and remove liquid outside by filter- 

 paper. Focus on the sediment, using a l / 5 -ijich objective, 

 then cut off nearly all light from below. When trans- 

 parent or hyaline casts are sought for swing the mirror to 

 one side and upward and throw the illumination upon the 

 slide obliquely or use a small diaphragm. They will be 

 more plainly visible by this means than with a strong illu- 

 mination. After the casts have been detected their cylin- 

 drical shape can be shown by inclining the stage of the 

 microscope so that they roll in the liquid. 



BACTERIA. 



The freshly-voided normal urine contains no bacteria. 

 They may be present, however, under abnormal condi- 

 tions, and will soon appear in normal urine .upon its stand- 

 ing exposed to the air. On account of the large amounts 

 of organic matter dissolved in the urine, it furnishes a 

 medium in which micro-organisms readily grow. This 

 occurs even in the bladder if they are introduced from 



