28o BACTERIA, YEASTS, AND MOLDS 



Does the dough rise as rapidly and as satisfactorily as when yeast is 

 used? Does the baked dough have the same taste? 



39. Kumiss. Into, a quart of milk put two tablespoonfuls of com- 

 mon sugar and add about one sixteenth of a compressed yeast cake. 

 Put in a warm place and leave for twenty-four hours. Cool and 

 taste. It will be kumiss, or fermented milk. Is it sour? 



Experiments illustrating Bacteria 



40. Putrefaction. Place in a series of test tubes, with a little 

 cold water, the following : (a) a bit of raw meat ; (b) some white of 

 egg ; (c) some flour ; (d) some crushed beans ; (e) sugar ; (f) starch ; 

 (g) a bit of melted butter. Set all of these tubes in a warm place 

 for two or three days and determine which will putrefy and which 

 will not. 



/41. Effect of Moisture. Place a little of the following foods in test 

 tubes: (a) dry beans; (b) Indian meal; (c) a piece of dry bread; 

 (d) graham meal ; (e) flour; (f) common crackers. In another series 

 of test tubes place the same materials moistened with water. Set 

 all aside in a warm place and notice the effect of water in bringing 

 about putre facliga. 



"^ 42. ^ffert oiE 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. 



>/^3. Effect of Boiling. Chop finely some raw beef and place it in 

 water, warming slightly but not heating it to more than 130°. 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. 



44. Effect of Freezing. The following experiment can be per- 

 formed only in cold weather. Place a little hay in water and heat to 

 a lukewarm temperature, leaving the same to steep for half an hour. 

 Filter through filter paper into two test tubes. Plug with cotton 

 and set one of the test tubes in a warm place. Put the other out of 



