Experiments

24. - Collection of mold for study.

a. Expose a piece of moist bread to the air of the room for about 10 minutes. Keep in a moist chamber and watch for the development of mold. A jelly glass inverted over the bread on a plate will do for the glass chamber.

b. Expose a dish containing a freshly opened baked potato to the air of the room for about 10 minutes. Cover; keep in locker and watch for the development of mold.

c. Bring into the laboratory anything that you can find on which mold is growing.

25. - Description of mold. Describe briefly the general appearance of these various forms under a small magnifying glass (15 diam.) or under a dissecting microscope (15 diam.).

Describe briefly the naked eye appearance of these various molds that appear in the laboratory.

26. - Mold on bread. Place several slices of bread under a bell glass or any dish that will protect it from evaporation. Battery jars, large beakers, or even common bowls will answer. Moisten the bread with water and put aside in a warm place (8o°-(900 F.). After two or three days the bread will usually show signs of white mold. Allow the mold to grow until some color appears and then determine, if possible, whether there are more than one species of mold on the bread.

27. - Molds on different foods. Under separate bell glasses place bits of cheese, some pieces of lemon, and a bit of banana. Each of these should be moist. Cover and put aside dish as in the last experiment. Molds will grow in a few days, but probably different species will grow upon the different materials. Compare the molds and determine how many kinds can be seen.

28. - Experiment to show the mycelium. Place a little fruit juice, such as may be obtained from canned fruit, in two tubes or in homoeopathic vials and drop a few mold spores from the last experiment, or a little dust from the floor upon the surface of the liquid. Set aside to grow and notice how the molds spread and send fine threads into the liquid. Later notice that colored masses of spores grow in the air upon the surface of the liquid but not in the liquid below.

29. - Spores. After the molds of the previous experiments have begun to produce spores, as shown by the appearance of some color, remove a little spore material from the surface with a knife blade or a platinum wire and examine under a microscope. For this purpose a compound microscope is necessary, since the spores are very small.

30. - Growth of mold from spores. Moisten a bit of bread and transfer with a platinum wire a little bit of the spore mass from a vigorously growing mold to the surface of the bread. Cover with a bell glass and set aside for growth. Examine every day and note that molds start from the points where the bread was inoculated with the mold spores.

31. - Mold spores in dust. Melt gelatin1 in 7 prepared test tubes, and pour it from each into sterilized petri dishes. Replace the cover upon the dish and allow the gelatin to harden. Label the petri dishes A, B, C, D, E, F, and G. Proceed as follows:

A. Sweep a little dust from the floor and scatter over the prepared gelatin in A. Replace the cover and allow the dish to remain in a cupboard until molds begin to grow. Note the number of hours or days until a growth appears. Obtain dust from the following sources and proceed as in A.

B. Dust from a crack in the flour.

C. Shake a dry duster over the gelatin.

D. Shake a damp duster over the gelatin.

E. Shake the hem of a skirt over the gelatin.

F. Expose a plate of gelatin to the air of the room while sweeping.

G. Expose a plate of gelatin to the air of the room 2 hours after sweeping and dusting thoroughly.

Note : The above experiments may be performed using moist bread instead of petri dishes of gelatin, but the results are not as impressive. Bread can be used, however, if gelatin is not at hand.

32. - The effect of drying. Place under separate bell glass two slices of bread, one of which is damp, either naturally or slightly

1Preparation of gelatin culture media: To 100 grams of gelatin add goo cc. of water and about 5 grams of Liebig's Extract of Beef and cook in double boiler for 5 minutes. While still hot filter the material through absorbent cotton. In using absorbent cotton for this purpose, a large funnel should be used and the absorbent cotton wet with hot water, placed in it. The liquid is poured into the cotton and it will run through readily, coming out as a tolerably clear solution. Some of the filtered jelly is to be placed in sterilized flasks and some in test tubes, about 10 cc. in each. Plug the flasks and test tubes with cotton and steam the jelly in a common steamer for 30 minutes. At the end of 24 hours it should again be placed in the steamer and steamed for half an hour. Once more set it aside for 24 hours and upon the third day steam it again for half an hour and cool. Material thus prepared should give a clear, slightly brownish jelly, which, if properly sterilized, will keep indefinitely. It should be acid to litmus paper.

moistened with water, and the other dried. Leave for two or three days and notice the effect of drying in preventing the growth of molds. If one slice remains dry, no molds will grow upon it though the other soon becomes covered.

33. - The effect of boiling temperature. In each of two test tubes of gelatin place a small quantity of mold spores. Melt the gelatin in the tubes at as low a heat as will melt it. Pour the contents of one tube into a petri dish and cover at once. Place the other tube in a beaker of boiling water and allow the water to boil briskly for half an hour, after which the gelatin is to be poured into a petri dish and treated like that in the first tube. Set both dishes aside for mold growth and examine at intervals for several days, noticing whether molds develop in both dishes or only in the first. If they grow in both, note the relative abundance in the two dishes.

34. - Effect of low temperature. Prepare two plates of hardened gelatin and sow mold spores upon the surface of each. Leave one in the ordinary room temperature and place the other in an ice chest or some other place where the temperature is low. Compare day by day, and determine the effect of low temperature in checking or stopping mold growth. Do any molds grow upon the dish placed in the ice chest ?

35. - Effect of air currents. Moisten a slice of bread and sow mold spores upon it, or allow it to mold spontaneously under a bell glass. After it shows a luxuriant growth of mold, remove the bell glass and leave it exposed to brisk currents of the air. Notice how the growth of the mold ceases and the delicate mycelium flattens down close to the bread.

36. - Molds in cheese. Obtain a bit of Roquefort cheese. Cut it open and remove a bit of the green mass in the middle by means of a knife point or platinum wire. Sow this substance upon the surface of a dish of hardened gelatin and set aside for growth. After two or three days, the molds will begin to develop and may be studied with a microscope. When they begin to produce spores, they should, if possible, be studied sufficiently to determine the species.