LA CURATOR V WORK IN DAIRY BACTERIOLOGY 297 



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. 



No. 32. Germicidal Action of Milk. Procure some milk fresh 

 from the cow; dilute I c.c. of this milk 100 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. 



No. 33. 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 

 a clean brush and then with a damp cloth. Wash the udder and 

 especially the teats with a 10% borax solution. After drawing 

 about a dozen jets on to the ground, remove the plug from the 

 flask and, placing its mouth very close to the teat, milk it about 

 half full, and replace the cotton plug. Carry at once to the 

 laboratory and make a litmus gelatin plate immediately, diluting 

 10 times. After 2 or 3 days' growth, count the colonies. Are 

 there any acid colonies of the Bact. lactis acidi present? If 

 time permits, isolate the colonies; purify and determine the 

 general class of bacteria. 



Allow the rest of the milk, to stand at about 70 to see if it 

 will sour normally. 



No. 34. Effect of Temperature on Species of Bacteria in Milk. 

 Procure some fresh milk and make several litmus gelatin plates, 

 diluting joo times. Divide the milk in three lots, placing one 

 at about 50, one at 70, and one at 98. At the end of 24 

 hours make plates from each, diluting that kept at 50 2,000 

 times, that at 70 10,000 and 100,000 times, and that kept at 98 

 500,000 times. After another 24 hours, make some plates from 



