SPECIAL EXAMINATIONS 381 



37 C. in a broth made by mincing i lb. of fat-free bullock's- 

 heart meat ; macerate it in cold water for two to three 

 hours ; cook over a small gas flame for two to three 

 hours more ; boil ; filter ; make up to a litre ; add 10 grm. 

 each of NaCl and Witte's peptones ; and standardize to an 

 acidity of 1-5 per cent to phenolphthalein. To obtain an 

 emulsion from the culture, it is well shaken and then 

 filtered through a double layer of Swedish filter-paper. 

 The carbolic acid dilutions were made at first by taking 

 ac. carbolic B.P. no grm. = 100 grm. pure phenol. Later, 

 dry crystalline carbolic acid was taken as 100 per cent 

 phenol. The dilutions were always freshly made, as it was 

 found that otherwise they lost some of their germicidal 

 power, even when kept corked and in the dark. The dis- 

 infectant dilutions are made with distilled sterile water, and 

 5 c.c. of each are put in small glass specimen pots, 2-5 in. 

 X f in., arranged in holes on a board. These pots are 

 left uncovered during the experiment, and the results are 

 not vitiated owing to the MacConkey's media used for the 

 subculturing, inhibiting most other organisms than B. coli. 

 Owing to the platinum spoon holding three times the 

 amount in a standard loopful, 10 c.c. are used for the 

 subculture medium. To assist in rapid work a special 

 wheel has been devised, to hold the spoons, when not in 

 use, in a sterilizing flame. 



Process. All the apparatus being ready and to hand, 

 the dilutions of the unknown disinfectant are " seeded," 

 each getting a spoonful of the B. coli emulsion, and being 

 well stirred. The seeding is begun at the strongest 

 dilution and proceeds to the weakest. At the end of 

 2-5 minutes, a spoonful is removed from the first dilution 

 seeded and added to a tubeful (10 c.c.) of MacConkey's 

 broth, properly labelled. The same process is repeated 

 with all the tubes, and is all gone over again after 5, 7-5, 

 10, 12-5, 15, 20, 25, and 30 minutes. 



The same procedure is followed with dilutions of carbolic 

 acid. 



The subcultures are incubated for forty-eight hours at 

 37 C. A positive result is indicated by the medium 

 turning red, and the formation of bubbles of gas. In 

 some tubes this change will appear in twelve to fourteen 



