40 GENERAL BACTERIOLOGY 



Instead of the hollow ground glass-slide an ordinary glass-slide 

 to which a small section of a glass or rubber tube has been cemented 

 can be used, and in some cases is preferable. 



In examining the preparation under a microscope, focusing is a 

 somewhat difficult process and must be carried out with great care. 

 Use a narrow diaphragm. Find the edge of the drop with the low 

 power (f in. objective), adjusting slide so that edge of drop passes 

 through the center of the field; then turn on the high power (-J- in. 

 objective) and focus without moving the slide. The edge of the drop 

 is selected because the bacteria are here nearest the cover-glass and 

 hence more easily focused upon than where they are deeper in the 

 drop. 



References. A. 204 ; H. 114 ; M. & R. 87 ; McF. 141 ; P. 209. 



Special Directions. 



a. Make a hanging-drop preparation of water containing parti- 

 cles of India ink or carmine in suspension. This illustrates molec- 

 ular or Brdwnian movement. 



&. Make a preparation using straw infusion or tartar from teeth 

 to note variations in rate and character of vital movement. 



c. Make hanging-drop preparation of B. suhtilis from agar or 

 bouillon (13). 



d. Make same preparation of B. coli (13). 



In eases where vital movement is questionable, remove the cover- 

 glass and place a drop of formalin or chloroform in the bottom of the 

 cell ; replace the cover-glass, examine and note change in character 

 of movement, if any. 



EXEECISE 22. MICEOSCOPICAL STUDY OF FORM TYPES. 



a. Make bouillon and agar streak ciiltures of the following or- 

 ganisms : 



Micrococcus (any species). 



Sarcina lutea Schroeter. 



Pseudomonas fluorescens (Fluegge) Mig. 



Bacillus mycoides Fluegge. 



Microspira Metschnikovi Mig. (or any vibrio). 



Spirillnm ruhrum v. Bsmarch. 



h. Incubate cultures at 2S° C. for 24 hours. 



