306 BACTERIA, YEASTS, AND MOLDS 



Does the dough rise as rapidly and as satisfactorily as when yuast 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 efEect of water in bringing 

 about putrefaction. 



42. 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. 



43. 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 



