GENERAL BACTERIOLOGY 79 



NOTE. Molds may be recognized by the filamentous, cotton- 

 like form of the colonies. The hyphae extending into the air 

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

 platinum needle, the spores may be transferred to an agar slant, 

 and development will take place. Colonies of yeasts or torulae 

 appear smooth, moist, opaque, elevated, and slightly yellowish- 

 white, or sometimes reddish. These may be transferred in the 

 same manner as colonies of bacteria. Molds require careful 

 handling for microscopical demonstration. They are usually 

 examined in water or glycerin in the unstained condition. 



EXERCISE 2 



Method of preparing molds for microscopical 

 examination 



1. Transfer some of the growth to alcohol (50 per 

 cent). 



2. When thoroughly moistened, transfer some of 

 the growth to a drop of glycerin on a slide. 



3. Spread carefully with a platinum needle. 



4. Cover with a slip and examine. 



5. If satisfactory, the preparation may be made 

 permanent by painting a ring of asphalt around the 

 edge of the cover slip. 



Molds may also be stained in the following manner: 



1. Place a small amount of mold on a slide. 



2. Cover with alcohol and allow alcohol to evapo- 

 rate. 



3. Wash in water. 



4. Stain with gentian violet or methylene blue. 



5. Mount in glycerin. 



EXERCISE 3 

 Study of Yeasts 



i. Examine a small amount of yeast taken from an 

 agar slant in water under the high power of the micro- 



