YEAST 105 



B. Mount a small quantity of the "■ fur '^ from the teeth fipread 

 out in a drop of water. A number of forms will be found* 

 (Strasburger-Hillhouse, Fig. 102). 



C . Study preparations from some of the brightly colored colonies (red, 

 yellow, pink, etc.) which may develop on the potato cultures, gener- 

 ally composed of very minute forms. 



D. Examine mother of vinegar (Sec. 101, B) for small rod-shaped types 

 {Bacillus aceti, with other forms). 



E. Study the growths from the infusion of decaying algae (Sec. 101, C) 

 for long, spirally twisted filaments of Spirochcete in very active move- 

 ment. 



103. Staining of bacteria. Stained preparations of bacteria frequently 

 show much more clearly tharn the living forms the structure of the cells and 

 processes of spore formation. The demonstration of cilia requires very 

 high powers and special methods. 



A. Mix a minute quantity of bacterial slime {Bacillus subtilis is a good 

 form) in a watch glass of water. Spread a film of the water on a cover 

 glass and allow it to dry. The process may be hastened by holding 

 the cover glass, film side up, well above a fiame ; the heat helps to 

 attach the bacteria to the cover glass. 



B. Dip the cover glass in a strong water solution of fuchsin or of gentian 

 violet. Rinse off the stain in water and examine to see if the bacteria 

 are overstained. If so, extract the stain with alchohol. Finally allow 

 the cover glass to dry and mount in Canada balsam. 



Questions. What types of the algse do the bacteria most 

 resemble in their cell structure and morphology ? How do 

 the bacteria obtain their food and what is its character ? 

 What changes have you observed produced by growths of 

 bacteria ? 



THE YEASTS, OR SACCHAEOMYCETES 



104. The culture of yeast.* * Prepare a pint of a five or ten per 

 cent solution of molasses in water. 



A. Place a small quantity of the solution in a test tube and 

 add a fragment of fresh yeast. The scum, or sediment, after 

 twenty-four hours will give excellent material of growing 

 yeast for microscopical study. 



