FUNGI 



195 



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

 lalf 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 

 '.)0F., and observe from time to time. When bubbles are rising rapidly, 

 conduct the gas into a vial of 

 imewater, as shown in Fig. 95, 

 noting that the same change 

 1 akes place that occurs when we 

 expire into lime water : 



CaO + CO 2 = CaC0 3 



Lime Carbon Chalk or 

 dioxide limestone 



Test the liquid by odor and 

 especially by taste. As soon as 

 fermentation is complete (that 



s, when the sweet taste has dis- 

 appeared), pour out half a pint 

 into a flat dish and set in a warm 

 >lace, protected from dust, to 

 study the formation of vinegar. 

 With the remainder attach the 

 lask to a small still, heat care- 

 :'ully, and test the first gill for 

 dcohol by taste, smell, and by 



burning. 



In doing this experiment dif- 

 r'erent members of the class, or 



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

 ,'orn 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 

 T _i__ of an inch or -g^oT of an inch in diameter. Let each 

 nember 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 

 opoch in control of disease that history records. Pasteur did 

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



FIG. 95. Testing the gas from yeast 

 fermentation with limewater 



