360 APPENDIX 



media will inhibit to a great extent the growth of the last 

 two groups and favor the development of the organisms 

 of the B. coli group. This group is by far the largest, 

 occurs most often and in greatest numbers in sewage and 

 like 'material, therefore tests for this group are used as indi- 

 cation of the presence of intestinal organisms in the material 

 (water in this case) to be examined. 



V. Litmus lactose bile salt medium. 



Bile salts are invaluable for certain media used for 

 water analysis as they inhibit organisms of practically all 

 but the intestinal type. 



20 gms. peptone. 

 5 gms. sodium taurocholate. 

 10 gms. lactose. 

 20 c.c. 2% azolitmin solution. 

 1000 c.c. distilled water. 



Method. 1. Dissolve the bile salt and peptone in the 

 water and boil. 



2. Add the lactose and sufficient azolitmin to give a 

 distinct purple tint. 



3. Filter, fill into fermentation tubes and sterilize by 

 intermittent method. 



Each student needs four litmus lactose bile salt fermentation 

 tubes. 



VI. Esculin bile solution for B. coli test. 



10 . gms. peptone. 

 5 . gms. sodium taurocholate. 

 0.1 gm. esculin. 

 . 5 gms. soluble iron citrate. 

 1000.0 c.c. distilled water. 



Method. 1. Dissolve the ingredients in the order given, 

 clear with egg albumen, tube and sterilize (see Prescott and 

 Winslow's Elements of Water Bacteriology, 3d Ed., p. 279). 

 This solution has a blue fluorescence. 



