DAIRY BACTERIOLOGY 87 



and pour into petra dishes. The number of colonies 

 that develop in each indicates the efficiency of the 

 disinfectant. The smaller the number of colonies 

 the more efficient the washing powder. 



Fig. 43. — Culture of 1-100 c.c. milk from average steril- 

 ized separator. 



Repeat, using a small speck of manure or dirt from 

 your finger nail. Also make plate cultures from a 

 drop of milk taken from a cow at beginning and last 

 part of milking. Make plate exposures by filling 

 petra dishes with melted agar and allowing to solidify. 

 Expose one, two, and three minutes in open air, 



