BACTEEIA OF WATER AXD SEWAGE 55 



C. Neutral Red bouillon. 



Add 1 cc. of the water under examination to tubes contain- 

 ing Xeutral Red bouillon. Fecal bacteria transform the 

 red color to a canary j'ellow accompanied by green fluo- 

 rescence. Make stains for B. coli. 



D. Phenol bouillon. 



Repeat C, using phenol bouillon. 



Exercise 78. Quantitative Examination of Sewage 



1. Procure samples as du-ected for water in Exercise 73. 



2. In making plates and fermentation tube tests use dilutions 

 of 1 : 1000, 1 : 10,000, 1 : 100,000, or even greater. 



3. ^lake plates of beef gelatin, beef agar, Heyden-XahrstofE 

 agar, and litmus-lactose agar. 



4. Incubate part of the agar plates at 37° C. and others below 

 22° C. Count the former after forty-eight hours and the latter 

 after sevent^^-two hours. Compare the results. 



Exercise 79. Bacterial Content of Snow and of Rain Water 



If opportunity presents itself, make bacterial counts of snow. 

 Collect samples in sterilized glass-stoppered bottles, as in case of 

 water. Bring the bottles to the laboratory, allow the snow to 

 melt, draw samples with sterile pipettes before all of the snow 

 has melted. Collect samples of freshly fallen snow and after 

 intervals of twenty -four, forty-eight, and seventy-two hours. 



Collect samples of rain water by uncovering sterile glass jars 

 while rain is falling. ]\Iake plate cultures within one hour from 

 the time the jars are set out. 



Compare the number of organisms per cubic centimeter with 

 that obtained in surface waters. 



Exercise 80. Study of Streptococci 



The term " Sewage Streptococci " is applied to a poorly defined 

 group including cocci which may or may not form well-defined 

 chains. Under the microscope they appear to occur in pairs, 

 short chains, or irregular groups. They grow well on sugar 



