LABORATORY WORK IN DAIRY BACTERIOLOGY 



After the above plates have developed count the colonies on 

 all the plates and compare. 



No. 38. Bacteria in Hay. Soak a little hay in warm (not 

 hot) water for an hour. Shake well and inoculate three litmus 

 gelatin tubes, the first with one, the second with two and the 

 third with three loops full of the hay infusion. Pour into Petri 

 dishes, incubate and study as usual. Compare the numbers of 

 liquefiers and non-liquefiers. Are there any acid forming 

 colonies ? , 



No. 39. Bacteria in Grain. Repeat the above experiment, 

 using some grain feed instead of hay. 



*No. 40. Value of Cleaning Milk Bottles. Procure 4 glass 

 bottles in which milk has been standing for a day; ordinary 

 unwashed milk bottles are best. 



a. Wash one with cold water. 



b. Wash one with hot water and soap. 



c. Wash the third and sterilize in steam. 



d. Leave fourth unwashed. 



Fill all four with fresh milk. Place all side by side at a room 

 temperature and notice the time of souring in each case. 



*No. 41. Bacteria in the Milk Pail. Place 100 c.c. of sterile 

 water in a milk pail that has received a simple washing. With 

 a little absorbent cotton rub this water around thoroughly ; allow 

 to stand a few moments, and, after another washing around the 

 pail, remove i c.c. of this water and plate in agar. Count the 

 colonies. 



a. Repeat, using (i) a dirty pail; (2) a pail simply steamed 

 for a few seconds in a steam jet, and (3) a thoroughly sterilized 

 pail. 



No. 42. Bacteria in Manure. With a sterilized platinum loop 

 transfer a small bit of either fresh or dried manure from a cow 

 to a sterile water flask. Mix thoroughly. Transfer two loopfuls 

 of the mixture to a tube of melted agar. Pour into Petri dishes 

 and after growth count the number of colonies. To determine 



