PROBLEM 103 121 



number 1 in the ice box, num})cr 2 in a dark box at a moderate tem- 

 perature, number 3 in a box at a hot temperature (100° F. or over), 

 and boil number 4 for 15 minutes and then place with number 2. 



Observations. — In which tube does the greatest amount of 

 growth take place? (Note the odor as well as color of bouillon.) 

 In which tube did the least growth take place? 



Conclusion. — What is the effect of intense heat upon bacteria? 



From this experiment we derive the very important mothnrl of 

 fighting bacteria by means of sterilization. From experiments 

 already performed give a definition of sterilization. 



Problem 102: To note the effect of moisture and drjjness 



upon the growth of bacteria. ( Home problem. ) 



Materials. — Beans, test tubes. 



Method. — Take two beans. Remove the skin and crush one. 

 Soak the second bean overnight and then crush it. Place in test 

 tubes, the first dry, the second with water. Leave both in a warm 

 place for two or three days. Then smell each tube. 



Conclusion. — 1. In which is decay taking place? 



2. In which tube are bacteria at work ? How do you know ? 



Note. — Heat and dryness are thus shown to be unfavorable to the growth of 

 bacteria. From experiments dry sterilization, if continued long enough and if the 

 heat is sufficiently high, seems the more eflfective. 



Some foods are spoiled by too great heat. Milk, in particular, 

 is changed by boiling so as to be quite a different food. Hence a 

 method of killing germs known as pasteurization is of importance. 



Problem 103 : To determine tlie effect of pasteuri z option upon 

 the keeping quality of milk. 



Materials. — Milk, two sterilized covered jars, thermometer, 

 double boiler, or pasteurizing apparatus. 



Method. — Place half of the milk in a sterilized jar, cover, and 

 leave in a warm place for 24 to 48 hours. 



Place the remainder of the milk in the other jar, cover, and put it 

 in the double boiler or pasteurizing ai)paratus. Bring the hot 

 water suriounding the jar from 160° to 180° F. for about 30 



