LABORATORY WORK 



301 



-what cloudy. Transfer a loopful of this material to a glass slide and 

 place upon it a cover-glass. Place the whole under a microscope, 

 preferably using a i /6-inch objective, and narrow the diaphragm 

 below the stage until most of the light has been cut off. Now focus 

 very carefully upon the bacteria under the cover-glass, and, if they 

 are motile, it will be seen that they are moving around through the 

 microscope field with more or less rapidity. If they are stationary, 

 it may be assumed that they have no flagella. This test requires 

 great care, for with some slowly moving forms it is not always easy 

 to detect the motion with certainty ; but it can easily be done with a. 

 little study. 



Fig- 73- 



w 



a b c d e 



Types of Gelatin Liquefaction 



a. Crateriform. i. Napiform. t. Infundibuliform. d. Saccate, e. Stratiform. 



12. Germicidal Action of Milk. Procure some milk fresh 

 from the cow; dilute i c.c. of this milk ioo times and make 6. 

 agar (or gelatin) plates. Cool the rest of the milk at once to- 

 70°. At the end of 2 hours make 6 more plates in exactly the same 

 way as above. In 2 hours more make 6 more plates. After proper 

 time for growth, count the colonies and determine whether there 

 has been a decrease in numbers of bacteria in the first few hours 

 after milking. 



13. Aseptic Milk. Sterilize a liter flask plugged with 

 cotton. Wash the hands thoroughly in hot water and soap, and 

 put on a clean milking suit. Remove a clean cow from the barn 

 into the open air, brush the dirt from the flanks and udder with. 



