PUTREFACTIVE ORGANISMS 113 



(2) Test for ammonia with Nessler's solution. 



(3) Find out when the nitrite disappears. 



Ex. 61. To a very dilute solution of egg albumin add a 

 dilute solution of ferrous sulphate to prevent coagulation; 

 sterilize at 100 C. Inoculate with pure cultures of 



(a) B. mycoides, 



(b) B. fluorescens liquefariens, 



(c) B. (Proteus] vulgare? 



and incubate at 30 C. for ten to fifteen days. 



(1) Test for ammonia with Nessler's solution. 



(2) Heat with magnesia and test the gases evolved with 



litmus paper. Compare with uninoculated sterilized 

 control tubes. 



Ex. 62. Chop in pieces a small piece of beef and place it in 

 a beaker of water. 



Leave in a warm place for twenty-four to forty-eight hours until 

 putrid. 



Examine a drop of the putrefying liquid for Proteus bacteria. 

 Note their lively motion. 



Stain some with gentian-violet. Inoculate gelatine and agar 

 plates with a drop of the putrid liquid diluted with sterile water 

 and observe the form of the colonies obtained. 



Ex. 63. The Indole Test. Prepare a 2 per cent, solution of 

 peptone; add to it J per cent, of common salt and make it 

 slightly alkaline with a drop or two of sodium carbonate solution. 



Place about 10 c.c. in a number of tubes and sterilize. 



Inoculate tubes with 



1. Bact. vulgare, 



2. Bact. coli, 



3. Bact. lactis aerogenes, 



4. Bact. fluorescent^ 



and incubate for six to seven days. 



1 Pure cultures of these and other organisms can be obtained from the 

 Author. 

 H 



