CULTURE-MEDIA. 



73 



The coagulation of milk, which is brought about by certain 

 bacteria, is a very valuable differential point. Litmus milk is 

 prepared as above and has added to it i per cent, of azolitmin 

 before sterilizing. This indicates whether or not acids are 

 formed by the bacteria which are afterward cultivated in the 

 milk. 



DUNHAM'S PEPTONE SOLUTION. 



Peptone 10 grams. 



Sodium chloride 5 grams. 



Water i liter. 



Boil, filter, sterilize in the usual manner. 



Nitrate Broth. Dissolve i gram of peptone in 1000 c.c. 

 of tap water, and add 2 grams of nitrite-free potassium nitrate. 

 This solution is distributed into test-tube, 10 c.c. in each tube. 



Broth for the Indol Test. Standard broth described above 

 may be used for this test provided it contains no muscle-sugar, 

 the muscle-sugar having been removed by cultivating B. coli in 

 the beef infusion for twenty-four hours previous to its prepara- 

 tion. Or the following solution may be employed for the test: 



Dunham's solution is valuable to test the development of 

 indol by bacteria (see Part II., Chapter II.). The develop- 

 ment of acids may be detected after the addition of 2 per cent, 

 of rosolic acid solution (0.5 per cent, solution in alcohol); 

 alakaline solutions give a clear rose-color which disappears in 

 the presence of acids. 



Blood-serum. The blood of the ox or cow may be obtained 

 easily at the abattoir. It should be collected in a clean jar. 

 When it has coagulated, the clot should be separated from the 

 side of the jar with a glass rod. It may be left on the ice for 

 from twenty-four to forty-eight hours. At the end of that time 

 the serum will have separated from the clot and may be drawn 

 off with a siphon or pipette into tubes. The tubes containing 

 the serum should be placed in a slanting position, as nearly 



