FUNGI 



195 



EXPERIMENT. To a quart of warm potato water, not filtered, add a 

 half pint of molasses and a yeast cake, previously mixed to a smooth 

 cream in a gill of fresh milk. Keep in a dark place at between 75 and 

 90 F., and observe from time to time. When bubbles are rising rapidly, 

 conduct the gas into a vial of 

 limewater, as shown in Fig. 95, 

 rioting that the same change 

 takes place that occurs when we 

 expire into limewater : 



CaO + CO 2 = CaCO 3 



Lime Carbon Chalk or 

 dioxide limestone 



Test the liquid by odor and 

 especially by taste. As soon as 

 fermentation is complete (that 

 is, when the sweet taste has dis- 

 appeared), pour out half a pint 

 into a flat dish and set in a warm 

 place, protected from dust, to 

 study the formation of vinegar. 

 With the remainder attach the 

 flask to a small still, heat care- 

 fully, and test the first gill for 

 alcohol by taste, smell, and by 

 burning. 



In doing this experiment dif- 

 ferent members of the class, or 



different class groups, may use different materials fruit juices, potato, 

 corn or rye mashes, malt decoction and thus add to the interest. 



Pure cultures. Before reading the next experiment try 

 hard to think how you would make a pure culture of a plant 

 __ 1 __ of an inch or -^o^-g- of an inch in diameter. Let each 

 member of the class write out his method and then compare 

 his result with those of the rest of the class. This is a test 

 and measure of power to think, imagine, and reason. When 

 Louis Pasteur first thought this out, he marked the greatest 

 epoch in control of disease that history records. Pasteur did 

 this first with the yeast plant in 1856. Up to this time 



FIG. 95. Testing the gas from yeast, 

 fermentation with limewater 



