40 
HOUSEHOLD BACTERIOLOGY. 
Requirements 
for Growth 
Products 
q( Growth 
Thus the generations are continued and the individuals 
multiplied. 
Yeast requires food, oxygen, warmth, and moisture. 
Sugary substances are especially liked by the yeast 
which is used to make bread. This is a specially cul¬ 
tivated form of brewer’s yeast. Yeast directly from 
FIG. 22. TYPICAL FORMS AND APPEARANCE OF BREWERS’ 
YEAST. (After Sedgwick and Wilson.) 
the breweries is often used for breadmaking. It 
is while feeding upon these sugary solutions that 
the tiny plants bring about the chemical changes by 
which alcohol and the gas, carbon dioxide, are pro¬ 
duced, The gas puffs Up the dough and makes pos^ 
