278 APPENDIX 



Tube Medium. The tube medium contains agar 5 gm., 

 gelatin 80 gm., sodium chloride 5 gm., meat extract 5 gm., 

 and dextrose 10 gm. to the liter of water; reaction +1.5. 

 The mode of preparation is the same as for the plate medium, 

 care being taken always to add the gelatin alter the agar 

 is thoroughly melted, so as not to alter this ingredient by 

 prolonged exposure to high temperature. The dextrose is 

 added after clearing. 



MILK 



The milk to be used as a culture medium shall be as 

 fresh as possible, " Certified Milk " being ordinarily the 

 best obtainable in city laboratories. It shall be placed in 

 a refrigerator over night to allow the cream to rise and 

 the suspended matter to settle. The skimmed milk shall 

 be siphoned off into a flask for use. It will be found more 

 convenient, however, to allow the milk to stand in a separa- 

 tory funnel. Should the milk be too acid the reaction shall 

 be corrected to +i by the addition of normal sodium hydrate. 

 It is then ready to be tubed and sterilized. Litmus milk 

 shall be prepared as above, with the addition of sterile i 

 per cent azolitmin. As it is impossible to make each lot 

 of litmus milk with the same shade of color, it is recom- 

 mended that a control tube be always exposed with the 

 inoculated tubes for purposes of comparison. 



NITRATE BROTH 



Dissolve i gm. peptone in i liter of tap water, and add 

 0.2 gm. of nitrite-free potassium nitrate. 



PEPTONE SOLUTION FOR INDOL TEST 



Broth which has been inoculated with B. coli to remove 

 the muscle sugar contains toxins which interfere with the 

 proper growth of many species, hence peptone solution, 



