314 PRACTICAL COURSE IN BOTANY 
10. Why does the use, for drinking purposes, of water that has been 
boiled render a person less liable to infectious diseases” (355.) 
11. Was the old-fashioned practice of handing the baby round to be 
promiscuously kissed by friends and neighbors a good one for the baby? 
(352.) 
12. Why is the spitting habit to be condemned? The use of common 
drinking cups in schoolrooms and other public places? (352.) 
13. Is it proper from a sanitary point of view that roommates at a board- 
ing school, or even members of the same family, should use soap, towels, 
and other articles of the toilet in common? (352.) 
B. YEasts 
Matsriau. — A piece of fresh baker’s yeast, some warm water, and a 
little honey or sugar solution; a pipette, or a medicine dropper; three or 
four clean pint bottles or preserve jars. 
To raise a crop of yeast fungi for observation, rub one fourth of a fresh 
yeast cake in water enough to make a paste; add one pint of water, with 
a tablespoonful of honey or sugar, and stir well. 
EXPERIMENT 96. WHAT CONDITIONS FAVOR THE GROWTH OF YEAST? — 
Pour equal parts of the liquid made as directed (see Material) into each 
of three pint bottles, stopper lightly, and label. Put (1) in a warm, dark 
place; (2) ina cool, dark place; and (8) in a bright light in a warm place. 
Observe at intervals of a few hours the changes that occur in each. Notice 
the bubbles that rise from the liquid. In which bottle do they form most 
rapidly? Lower a lighted match into it, or transfer some of the gas with 
a pipette into a vessel containing limewater, and tell what it is. Taste 
some of the fermenting liquid. Is it sweet? What has become of the 
sugar that was put into it? 
356. Yeasts and ferments. — Yeasts belong to a very dif- 
ferent order of fungi from the bacteria, but on account of 
their simplicity of structure and the similarity of their action 
to that of some of the latter, it is usual to consider them to- 
gether. They are the active agents of fermentation, and 
include a large number of species. The kind used for house- 
hold purposes is the same as that employed in making beer. 
Of this species there are many varieties, each one of which 
gives a characteristic taste to the beer made from it; and 
brewers, by paying attention to the cultivation of yeasts, 
give their product the special flavors peculiar to the different 
