DAIRY BACTERIOLOGY 85 



Exercise I, sterilize all empty glassware for at least 

 thirty minutes at a temperature of 212 F. in a dry 

 air sterilizer. After turning off the gas allow uten- 

 sils to remain in sterilizer for ten minutes before 

 opening the door. Otherwise the cool air coming 

 suddenly in contact with the hot glass may cause 

 some of the parts to crack. 



Before sterilizing pipettes wash each one thoroughly, 

 and while the ends are moist roll a piece of clean 

 cotton to a point and insert in the end of pipette. 

 Turn the remaining part of the cotton back over the 

 pipette, and if the latter is moist it will wrap tightly 

 around the same between the thumb and fore-finger 

 while revolving the pipette with the thumb and fore- 

 finger of the other hand. Repeat the operation with 

 the other end of the pipette. 



When using sterile pipette hold in vertical position 

 and pull lower plug first. This prevents contami- 

 nation to a great extent. 



The media must all be sterilized in a steam sterilizer 

 in order to prevent evaporation. Sterilize at 212 

 F. thirty minutes for three consecutive days to kill 

 all bacteria which are likely to germinate from the 

 spores which resist boiling temperature. 



Make a quantitative analysis of bacteria in a 

 sample of whole-milk by drawing into a delicately 

 graduated pipette .1 c.c. of the milk to be analyzed. 

 Transfer this into a sterile water blank test tube 

 containing .9 c.c. of sterile water. After shaking 

 well, transfer .1 c.c. of this in the same way to a test 

 tube containing sterile melted agar media. Mix 



