68 LABORATORY BACTERIOLOGY 
EXERCISE XIX 
A STUDY OF BACTERIA IN MILK 
100. It is desirable to understand somewhat clearly the 
bacterial contents of milk and to know something of the 
physiological properties of these bacteria. For this reason 
the bacteria in ordinary market milk should be studied, though 
briefly. 
101. Work for this exercise. Examine the plate cultures 
made from milk. Describe the different kinds of colonies and 
state approximately the number of each. Examine micro- 
scopically the bacteria in one of each kind of colony and 
determine its genus. 
Inoculate a tube of milk and one each of bouillon, agar, and 
gelatin from each of 3 different kinds of colonies, stating the 
genus of the bacteria in each. 
Inoculate group A of media from a culture of B. prodigiosus 
furnished. 
Make, for examination at the next and following exercises, 
3 gelatin plates from a sample of water furnished (unfiltered 
creek or well water), using for each culture the quantity des- 
ignated by the instructor. The quantity will depend upon the 
condition of the water. 
