Il6 LABORATORY BACTERIOLOGY 



EXERCISE LX 



THE QUANTITATIVE BACTERIOLOGIC EXAMINATION OF 



WATER 



171. This is to determine the number of bacteria in water. 

 In preparing media for this purpose the directions given in the 

 Journal of the American Public Health Association for Jan., 

 1898, p. 60, should be followed. The conditions of tempera- 

 ture and of media which favor growth differ for different 

 species. Many water bacteria will not grow at the incubator 

 temperature, while others which may be in it grow very slowly 

 at the room temperature. To determine numbers, it is better 

 to grow the bacteria in gelatin plates at the temperature of the 

 room. (In an actual examination a much larger number of 

 plate cultures should be made than can be managed here.) 



172. Work for this Exercise. — Make from the properly 

 collected water ^ gelatin plates, using a definite quantity of 

 water for each. To begin with, it may be safe to inoculate 

 these tubes with o.i^ o.25,(o.5(5,|and-faaiEcx:, respectively. 



To determine if there are gas-producing bacteria, and the 

 approximate number of these if any, inoculate ro lermehwtion 

 tubes with o.i c.c. each and 5 with \ c.c. each. In place of 

 the fermentation tubes glucose agar may be used. In this case 

 I fermentation tube of glucose bouillon should be inoculated 

 with 3 'c.c. of the water to determine the quantity of gas pro- 

 duced if there is any. If a large fermentation tube is used, add 

 5 c.c. of the water. 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 bacteriologic examina- 

 tion have already been given and this is largely in the nature 

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



