EXERCISE XXIX. 



BACTERIA IN MILK AND WATER. 



It is important to know something of the bacterial con- 

 tents of water as it is found in wells and streams and to 

 compare the bacteria ordinarily found in water with those 

 present in freshly drawn milk. It will be observed that the 

 normal bacterial flora of water and of milk are quite 

 different. 



References. — Microorganism in Water, by Percy and 

 G. C. Franklin. Clark and Gage, 34th Annual Report 

 State Board of Health of Massachusetts. Jordan, the 

 kinds of Bacteria found in River Water. The Journal of 

 Hygiene, Vol. Ill, No. i, (1903.) 



Work for this Exercise. — ^ Carefully examine and 

 describe the milk cultures made from the colonies on the 

 milk plates in the last exercise. 



Examine and describe the colonies on the plate cultures 

 made from water. Determine the number of colonies and 

 approximately the number of each kind of colony on the 

 plate. Estimate the number of bacteria in a cubic centime- 

 ter of water. This is done by multiplying the number of 

 colonies on the plate by the number of cubic centimeters of 

 water used for each plate. 



Examine microscopically the bacteria from one of each 

 kind of colony and determine the genus. 



Inoculate a tube of niilk and one of gelatin from each 

 of three different colonies, if there are so many. In later 

 exercises examine these cultures and compare them with 

 those made from colonies of milk bacteria. 



Examine and describe the cultures of B. prodigiosur. 



Inoculate group A and B of menia from a culture of B. 

 fluorescens liquefaciens furnished. 



