TEAST 37 



Florence flasks (bottles may be used), and into 

 each put about one litre of Pasteur's solution 

 with sugar. Into the first put also 200 c.c. of 

 fresh yeast. Close the mouth of each flask with 

 a plug of cotton -wool. Wrap each flask in a 

 cloth, or, better, in cotton, and put them side by 

 side in a box to protect them from draughts. 

 "When fermentation becomes vigorous in the first 

 flask, as will be indicated by the formation of 

 bubbles of gas, take the temperature of the liquid 

 in each flask with a good thermometer and com- 

 pare the results. In which flask is the tempera- 

 ture higher ? Let the flasks stand until about ten 

 or twelve hours after the formation of bubbles 

 has ceased in the first flask, and then take the 

 temperature again. "Was the difference in tem- 

 perature flrst noticed due to the presence of yeast 

 or to its growth ? "Why ? 



Effect of filtered yeast xipon a fermentable fluid. — 

 Sterihze a small porous porcelain cup, such as is 

 used in batteries, by boiling it in water for sev- 

 eral minutes. Set the porous cup into a teacup 

 which has also been boiled, and fill the porous 

 cup about half full of fiuid yeast. In a short 

 time some of the fluid part of the yeast will filter 

 through the porous cup, leaving the solid part 

 (yeast cells) behind, and will be caught in the tea- 

 cup. Fill a test-tube one -third full of Pasteur's 

 solution with sugar, plug the mouth of the tube 

 lightly with cotton -wool, and sterilize the con- 

 tents by boiling for about five minutes over the 

 flame of an alcohol lamp or a Bunsen burner. 

 AUow the fluid to cool, then with a glass rod, 



