87 



the fermentation tubes glucose agar can be used. In this 

 case one fermentation tube of glucose bouillon should be in- 

 oculated with 5 c. c. of the water to determine the quantity 

 of gas produced if there is any). From the gas produced in 

 these tubes determine approximately the number of the gas 

 producing bacteria. 



Careful and full notes should be taken on this examination 

 the preliminary methods for making a bacteriological exam- 

 ination have already been given and this is largely in the na- 

 ture of an investigation by each student. It is not expected 

 that the special methods other than those used in the lab- 

 oratory for pathogenic bacteria will be tried. 



§ 154. Collecting water. If the water is collected from 

 a spicket or pump allow it to flow for 2 or 3 minutes first 

 and then collect the desired quantity, 100-200 c. c. in a ster- 

 ile bottle and cork tightly, or if near at hand, absorbent cot- 

 ton plugs may be used. 



If from a stream or river withdraw the stopper and im- 

 merse the sterile bottle, to the depth desired and allow it to 

 fill. There are several mechanical devices for collecting 

 water from considerable depths from the surface. 



EXERCISE IvVII. 

 THE QUANTITATIVE EXAMINATION OF WATER (continued). 



§155. General directions. Examine the cultures and 

 count the colonies on the plates and estimate from them the 

 number of bacteria in a cubic centimeter of the water. That 

 is if there are 40 colonies on the plate containing . i c.c. of 

 water there are 400 bacteria in i c.c. of it. 



From the cultures in the glucose media estimate the num- 

 ber of gas producing bacteria present. 



Describe the appearance of the different colonies and indi- 

 cate the approximate number of each kind. 



