86 GENERAL MICROBIOLOGY 



6. Let dry. If desired the specimen may be mounted 

 in Canada balsam before examining. 



7. Examine with either the 1/7 or the oil immersion 

 objective. 



8. Write the name of the organism, the date, and your 

 name on the glass with India ink. 



By the use of the Chinese ink preparation, it is possible 

 to examine any organism unstained. Organisms so treated 

 neither shrink nor in any way change their form, making 



FIG. 31. Chinese Ink Preparation. (Orig. Northrup.) 



accurate measurement possible. Stains often cause organ- 

 isms to appear swollen or shrunken. 



The motility of bacteria may be more easily demon- 

 strated by adding a very slight amount of this ink to a 

 hanging drop of the organism being studied. 



Caution. Chinese ink is very expensive. When making 

 preparations, use every precaution to keep your supply 

 sterile, as contaminating organisms may be confused with 

 the culture under study. A control preparation to which 

 no microorganisms have been added will serve to detect 

 their presence, 



