8o LABORATORY GUIDE IN BACTERIOLOGY 



scope. Note the manner of reproduction by "bud- 

 ding." 



2. Prepare a culture in liquid wort of Sacch. cere- 

 visiae. 



3. Pour the supernatant liquid of the 24-hour-old 

 culture off, and spread the sediment on a gypsum block 

 with a looped needle. 



Note. — Gypsum blocks may be prepared in the following 

 manner: Gypsum (plaster of paris) is mixed with half its volume 

 of water and quickly placed in a cylinder of paper. When dry, 

 the paper is cut away and the block is placed in a suitable vessel 

 (a stender dish or a deep, narrow petri dish, covered by an 

 inverted tumbler). The block and vessel are then sterilized in 

 the hot-air sterilizer for one hour at 110° to 115° C., or in the auto- 

 clave for 30 minutes. 



4. Pour enough distilled water around the gypsum 

 block to submerge about one-half of it. 



5. Incubate at 25° C. 



6. Set aside in a cool, dark place for 3 or 4 days. 



7. Examine a small portion of the film on the surface 

 of the gypsum under the microscope in water. 



Note. — Under favorable conditions, and in the presence of 

 oxygen, yeasts will develop spores. The porosity of the gypsum 

 block, which admits free communication with the water, and the 

 fact that the surface of the block is exposed to the air, offer 

 favorable conditions for spore formation, which takes place in 

 3 or 4 days. 



EXERCISE 4. CULTURE STUDIES OF YEASTS AND MOLDS 



Make transfers from all agar cultures of yeasts to 

 wort gelatin and liquid wort. Mark these cultures 

 with labels or glass pencils on the side of the tube op- 

 posite to the slanted surface and just below the cotton 



