Experiments Illustrating The Action Of Bacteria

37. - Putrefaction.

Place in a series of test tubes a, b, c, d, e, f, g, h, with a little cold water, the following: a - a small piece of chopped raw meat b - a small amount of white of egg c - 1/4 tsp. bread flour d - 1/4 tsp. cornstarch e - 1/4 tsp. cane sugar f - a small amount of ground dried peas g - 1/4 tsp. melted butter h - 1/4 tsp. olive oil.

Cover each test tube with a piece of cheesecloth or stop with cotton.

Place all the test tubes together in a warm place for three days and watch to determine which will putrefy and in what order.

Putrefaction can be detected by the disagreeable odor and slimy condition of the water.

38. - Effect of moisture. Place a small amount of the following foods in dry test tubes a, b, c, d, e, f.

In a duplicate series place the same foods, but moisten each with water.

Allow all to remain in a warm place and compare at the end of 3 days.

Notice the effect of the water in evidently promoting putrefaction.

Foods - dry and wet.

a - dried crushed peas.

b - oatmeal c - bread d - entire wheat flour e - bread flour f - graham cracker

39. - Effect of temperature. Place bits of meat with a little water in three test tubes. Put the first tube in an ice chest, the second in ordinary room temperature, and the third close to a stove or radiator where the temperature is high. Notice the rapidity of putrefaction in each case.

40. - Effect of boiling. Chop finely some raw beef and place it in water, warming slightly, but not heating it to more than 1300 F. Divide into two parts, place each in a test tube, setting one aside without further treatment, but bringing the other to a brisk boil for a moment and then setting beside the first. At the end of twenty-four hours, examine to determine if putrefaction has occurred.

Effect of freezing. A visit to a cold storage plant with subsequent discussions will be more beneficial than an experiment to show the effect of freezing upon bacteria.

Experiments Illustrating Yeasts As Related To Fruits And Sirups

41. - Fermentation of cider. Grind up a few apples and strain the juice from the same by squeezing through cheesecloth. Collect the juice in test tubes and allow it to stand for a few days. A fermentation soon appears and the juice turns to cider. Examine the sediment with a microscope and detect the presence of yeast. Close up the tube with a cotton plug and leave it for a number of weeks, determining whether it subsequently becomes acid by the development of acetic acid.

42. - Fermentation of grape juice. Proceed as above, using grapes instead of apples. The juice will become wine if fermentation occurs properly.

43. - Effect of temperature. Prepare 3 tubes with molasses and water as above described and inoculate each with 3 drops of yeast in water. Place one tube in a refrigerator, a second in a moderately warm temperature, above 700 F., and a third in a warmer place, near a stove or radiator (temp, about 900 F.). Compare the three at the end of three, six, and twenty-four hours, and note the effect of temperature upon growth.

44. - Effect of light. Prepare two tubes in the same way and set one in a bright light and the other in a dark place. Keep both tubes at the same temperature and determine whether light has any effect upon the rapidity of growth.

45. - Make a small cavity in the surface of a glass of jelly. Place a drop of fermented grape juice in the cavity, replace the paraffin and tin covers, and allow the jelly to remain in a dark cupboard.

Examine after three days and notice the changes which have occurred in:

1. taste

2. odor

3. consistency

46. - a. Allow jelly to remain uncovered for a few minutes after it has cooled. Place the tin cover on jelly glass and set aside in warm, dark place.

b. Examine daily for growths which will soon appear.

c. Try to determine what kinds of mold appear.1 d. What is the coral pink mass which will probably appear?

e. Allow the action of microorganisms to continue until the jelly becomes semi-liquid. Place it in a bottle and cork tightly.

f. Keep the bottle in a warm place and notice the changes taking place.

g. What are the bubbles and froth which appear when the cork is removed?

h. What microorganisms other than molds have been at work?

47. - a. Partly fill a sterile jar a with hot peaches and sirup just ready for canning. Repeat in a second jar b.

b. Adjust the rubber band and seal a to keep out the air. Omit the rubber band on b, but clamp down the cover.

c. Place a and b together with a jar filled and sealed and containing no air bubbles in a warm, dark place. Compare daily for signs of the action of microorganisms.

1 An idea of the probable kind may be obtained by noting color and general appearance and comparing with what has already been learned. For actual identification the "key" at the back of Buchanan's Household Bacteriology will be found most useful.

d. Compare a and b. Why should a show molds when the outside air is excluded ?

e. Why does no change occur in the third jar?

48. - From these experiments what conclusions do you make as to: a. The covering of jelly or jams with hot paraffin or paper wet in alcohol.

b. The exclusion of air or air bubbles from a canned mixture.

c. The rate of action of microorganisms in a solution as jam or jelly compared with that in a sirup as canned peaches.

d. In what way can sugar in large amounts act as a partial preservative of fruits ?