5. Fit the tube with a one-hole rubber stopper through which passes an elbow tube. As 

 the gas escapes through the tube, cause it to bubble up through limewater contained in an- 

 other test tube, (a) Observe any change in the appearance of the limewater. (b) What 

 kind of gas is being given off?* 



Part C. Bacteria. 



6. Allow a small piece of meat to decay in a glass of water. After a day or two, examine 

 a drop of the water under the highest power of the compound microscope obtainable. This 

 will usually be sufficient to show bacteria*as minute specks, many of which may be seen swim- 

 ming rapidly about under the field of the microscope, (a) Observe any variation in the shape 

 of these minute plapts. (b) Compare their size with the' size of the yeast plants, (c) Make 

 a drawing showing as accurately as possible the yarious shapes observed. 



7. A culture medium for experimenting with moulds and bacteria may be prepared as 

 follows: Cut from a sound potato, six rectangular pieces (JigxJ^xlJ^ inches). Place the 

 pieces of potato in separate test tubes and add just enough water to cover ther.i. Use dry ab- 

 sorbent cotton as stoppers for the tubes. After stoppering the tubes with cotton, stand them 

 in a water bath or double boiler and boil for a minute or two. Set aside and boil again on two 

 successive days, pouring off the water after the last boiling. Read carefully, experiments 8, 

 9, 10, 11, 12, and 13. (a) Why boil the test tubes and potato pieces? (b) Why stopper the 

 tubes with cotton? References: Bacteria, Yeasts, and Moulds, Ch. XII. 



**8. Collect a little dust from the surface soil in the garden or from a flower pot. 

 Sprinkle a very little over the potato in one of the tubes. Stopper carefully with the cotton 

 and set it aside where it will have a temperature of from 80 to 95° F. (a) After twenty-four 

 hours, examine the potato within the tube to see if there are any festered patches, bacterial 

 colonies, on the surface of the potato. Record the time and results of your observation, (b) 

 Examine again at the end of another twenty-four hour period, recording results as before, (c) 

 Examine again at the end of a third twenty-four hour period. Record results. 



9. Collect a few very small particles of garden soil from a depth of six inches. For fur- 

 ther directions see Experiment 8. 



9 10- Perform Experiment 8 but instead of setting it aside where it will have a temperature 

 of from 80-95" F. place it where it will have a temperature near freezing. 



11. Brush the leaves of some plant over the mouth of the tube. Follow directions given 

 in Experiment 8. 



12. Introduce a house fly into a tube and keep it there until you see it walk on the potato. 

 Then allow it to escape. For further directions see Experiment 8. 



13. Unstopper a test tube for a moment in the hall while classes are moving. Restopper 

 the tube and set aside in your locker. Make observations and record as directed in Experi- 

 ment 8. 



14. Place some very dry bread crumbs in a dry petri dish. In another petri dish place 

 some wet bread crumbs, (a) After a few days observe any difference between the bread 



•Alcohol is also a product of fermentation caused by yeast plants. 



"The student should perform experiments 8, 9, 10, 11, 12, and 13 outside of school hours, at home or wherever 

 convenient. He should bring in a written report of the results of his experiments at the first laboratory period fol- 

 lowing the time required to perform the experiments. 



28 



