164 LABORATORY METHODS OF 



METHOD OF STERILIZING. 



Place the vessels in the sterilizer and light the gas; 

 watch the thermometer; keep the temperature up to 

 135 degrees C for one hour; then shut off the gas and 

 let the temperature go down to 45 degrees C, and then 

 open the door and take the vessels out. Store in the 

 locker till wanted. 



Light is another factor in the growth of bacteria. 

 It is a very decided germicide to certain bacteria. 

 It is probably the ultra violet and green rays that do 

 the killing of the germs. But light and heat both are 

 more certain to kill them than either heat or light 

 alone. Muir and Ritchie. 



Movement of Bacteria. This is variable. Some 

 will move wlien they are in the act of reproducing. 

 In what is commonly called the spore stage some 

 move more rapidly than at other times ; some less. 

 Some substances will cause bacteria to move towards 

 them, such as salts of potassium and sodium. This 

 property is called CHemiotaxsis, positive and negative. 



The Part Played by Bacteria in Nature. As has 

 been said, the function of bacteria is to break up the 

 complex molecule into more simpler ones, as shown 

 by the souring of milk, the curdling of cheese and 

 the fermentation of sugar solution. 



