36 
LABORATORY EXERCISES 
ance. What causes the murky appearance? What else is present 
in the yeast cake and hence in this mixture? What is the use 
of this starch? 
II. Structure. Study a drop of the mixture which has been 
mounted under high power. Note the size, shape, and color of the 
yeast plants. Observe their structure. (See Waggoner, Fig. 122.) 
Is protoplasm present? What is its nature? Note the large semi¬ 
transparent object within the cell. This is a vacuole. Make a 
drawing of a yeast plant showing its structures. 
III. Reproduction. What is the explanation of the several 
types of cell clusters? What becomes of the small “ huds ” (Dis¬ 
cussion by instructor or reference to text. Page 194.) What other 
form of reproduction may occur in yeasts? (Discussion.) Show 
by a series of drawings the manner in which yeast multiplies by 
budding. 
EXERCISE 41 
YEAST — FERMENTATION 
Use the yeast mixture which was prepared for the preceding 
exercise or a similar one. 
Number five fermentation or test tubes. In each, place 5 cc. of 
this mixture. To No. 1, add nothing; to No. 2, glucose; to No. 3, 
cane sugar; to No. 4, starch; and to No. 5, glucose. Boil No. 5. 
Fill each with water and allow to stand in a warm room. At the 
end of several hours observe the results. Note the amount of gas 
in No. 2. The amount of gas present indicates the amount of 
growth of the yeast plants. This gas may be tested for the presence 
of O and CO 2 . What is the gas? What is its source? Smell the 
contents. What else besides CO 2 is present? What has caused 
these changes in the contents of this tube? The process is known 
as alcoholic fermentation. Compare the amount of fermentation 
in the other tubes with that found in No. 2. (Compare with 
Waggoner, Fig. 125.) What substances ferment? What is the 
effect of heat upon fermentation? Explain. What bearing does 
