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 ( 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 Brownian movement. 



ft. 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. subtilis from agar or 

 bouillon (13). 



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



In cases 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. 



EXERCISE 22. MICROSCOPICAL STUDY OF FORM TYPES. 



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

 ganisms : 



Micrococcus (any species). 



Sarcina lutea SCHROETER. 



Pseudomonas fluorescens (FLUEGGE) MIG. 



Bacillus mycoides FLUEGGE. 



Microspira Metschnikovi MIG. (or any vibrio). 



Spirillum rubrum v. ESMARCH. 



I. Incubate cultures at 28 C. for 24 hours. 



