CHAPTER VIII 



STUDY OF YEASTS, MOLDS, AND TORUL^ 

 EXERCISE 1. CULTURAL STUDIES 



Read carefully the chapter on yeasts and molds in 

 the textbook. Yeasts, torulae, and molds grow better in 

 a medium of a slightly acid reaction than in a neutral or 

 alkaline medium. Wort-agar or gelatin prepared as 

 described (Appendix I) will answer very well for this 

 purpose. 



1. Melt eight wort-agar tubes in the water-bath. 



2. Pour the contents of two tubes into sterile Petri 

 dishes, and set aside to solidify. 



3. Allow the other six tubes to solidify so as to form 

 a slanted surface. 



4. After the plates have cooled, expose them to the 

 air in two different places for 10 or 15 minutes. 



5. Place in your locker. 



6. Examine after 24 or 48 hours. Describe what 

 you see. 



7. Transfer several mold and yeast colonies to the 

 slants prepared. 



8. Make transfer of a stock-culture of Saccharo- 

 myces cerevisiae, or any other species of yeast. 



Note. — Molds may easily be recognized by the filamentous, 

 cotton-like form of the colonies. The hyphse extending into the 

 air carry the spores (conidia). By gently touching these with a 

 sterile platinum needle, the spores may be transferred to the 

 agar-slant, and development will take place after 24 hours. 

 Colonies of yeasts or torulee appear smooth, moist, opaque, 

 elevated, and slightly yellowish-white, or sometimes reddish. 



49 



