EXPERIMENTS 293 



b) At end of 24 hrs., examine some of sediment a under 

 microscope, using the high power. 2 Note yeast cells with their 

 buds. Make sketches of characteristic forms and compare with 

 forms in the yeast cake. 



c) Collect gas given off by fermentation, by closing mouth of 

 test tube with a cork in which is inserted a bent glass delivery 

 tube, and identify it. 



2) Influence of temperature upon activity of yeast: 



a) Prepare a test tube similar to 1, a), but put it upon ice 

 for 24 hrs. Compare with 1, a), and note differences. 



b) Prepare 3 test tubes similar to 1, a). Place one in water 

 at 150 F. for 10 min.; label and place with 1, a). Place 

 second in water at 175 F. for 10 min.; label and place with 

 other two. Boil third gently for 10 min. ; label and place with 

 others. At end of 24 hrs., compare 3 test tubes of this experi- 

 ment with test tubes of 1, a) and 2, a). 



3) Presence of yeast in air: 



a) Prepare 3 test tubes similar to 1, a), except that no 

 yeast is added. Put tubes uncovered in various parts of room 

 and leave uncovered for a day or two. Note whether there is 

 any fermentation. When bubbling begins, examine sediment 

 under microscope, to detect yeast. 



b) Examine also squirming rods and other forms of microbes 

 present. 



4) Putrefaction through activity of microbes: 



a) Place in a test tube a small piece of raw meat. Add some 

 cold water and set aside in a warm place for 2 or 3 days, noting 

 changes from day to day. At end of time, note odor and ap- 

 pearance of both meat and fluid. 



b) Examine sediment under microscope and note various 

 forms and degrees of activity of microbes present, a 



1 The sediment is best obtained by introducing into the liquid a 

 glass tube drawn out to a moderately fine point at one end. Hold 

 the other end closed with the finger until the fine end reaches the 

 sediment. Then allow the air to escape from under the finger tip. 

 The sediment will then enter the small tip. 



2 The best results are obtained by using a -^ in. oil immersion 

 objective, which can probably be borrowed, if necessary, from a 

 physician. 



To stain these microbes, which are chiefly bacteria, in order 

 more clearly to show their forms, various coloring fluids may be 



