BACTERIA 109 



How is this indicated? Do any of the colonies have any 

 effect on the gelatin? 



2. Surrounding Conditions and Growth. Into tubes of 

 bouillon introduce several drops of fluid from some culture 

 of bacteria and treat the tubes as follows : 



(a) Close the tube with a plug of cotton. 



(6) Close the tube with cotton and boil for five minutes. 



(c) To a third tube add a small portion of a poisonous 

 substance, such as corrosive sublimate or formalin. 



(d) Place some tubes in the bright sun and others in the 

 dark; place some on ice and others in a warm place. 



Label all the tubes and set away for a day or more. Ob- 

 serve and note changes, if any, as indicated by the odor 

 and cloudy appearance of the culture fluid. Explain the 

 differences. 



