106 TYPE STUDIES 



B. Shake half a yeast cake in a pint of molasses solution and 

 place in a bottle inverted over a dish of water. Note the 

 fermentation indicated by the formation for several days of 

 bubbles of gas, which will collect in the upper region of 

 the inverted bottle. Test the nature of this gas by the aid 

 of limewater in the manner described in Exp. IV. What is 

 the gas ? Note the decided odor of alcohol in the fluid after 

 fermentation has ended. 



C. If convenient distill off about a quarter of the fermented liquid, add 

 a little quicklime to the distillate, and redistill into a carefully cooled 

 receiver. Pour some of the second distillate into a saucer, note its 

 odor, and try to light it. 



105. Structure of the yeast cell.* ^ 



A. Mount in water some of the scum, or sediment, present in 

 the culture described in Sec. 104, A. Brewer's yeast, if 

 obtainable, is perhaps the best form for microscopical study, 

 especially the " top yeast." Observe the colorless oval cells 

 frequently occurring in short chains or small groups. These 

 are yeast cells. Make drawings to show : 



1. A large cell with granular protoplasm containing one or 

 more vacuoles. 



2. The formation of new cells by the process of budding. 

 Draw stages in the development and growth of the buds, 

 and the formation of chains or clusters of cells. 



B. Mount a bit of yeast cake in water. Stain with iodine. 



1. What are the large grains composing the bulk of the 

 yeast cake ? 



2. What is the staining reaction of the yeast cell with 

 iodine ? Is there starch in the cell ? 



Questions. What are the life habits of the yeast plant ? 

 What is its food and how do the cells obtain it ? Can the 

 yeast cell absorb soli4 food like an Amoeba ? Why ? What 

 happens during the process of fermentation ? What part 

 does yeast play in the raising of bread ? What substitutes 

 for yeast may be employed in bread making, and why? 



