I QO MEDICAL BACTERIOLOGY 



MEDIA 



Standard extract broth is used, both for the culture to be tested and for the 

 subcultures made after exposure to the disinfectant. The broth is made from 

 Liebig's extract of beef and is in exact accordance with the standard methods 

 adopted by the American Public Health Association for water analysis. Ten 

 cubic centimeters of the broth are put into each test-tube. This amount of 

 broth has been found sufficient to avoid any antiseptic action of the disin- 

 fectant carried over. It is important that the reaction of the media is just 

 + 1.5. 



ORGANISM 



For the test organism a 24-hour-old broth culture in extract broth of the 

 B. typhosus (Hopkins) is used. Before beginning a test the culture should be 

 carried over every 24 hours on at least 3 successive days. For carrying over 

 the culture one loopful of a 4-millimeters platinum loop is used. 



Before being added to the disinfectant the culture is well shaken, filtered 

 through a sterile filter-paper, and placed in the water bath in order that it may 

 reach a temperature of 2oC. before being added to the disinfectant. 



TEMPERATURE 



A standard temperature of 2oC. has been adopted for all experiments. 

 This temperature is obtained by the use of a specially devised water bath. The 

 culture and dilutions of the disinfectant are brought to this temperature before 

 the beginning of the test. 



PROPORTION OF CULTURE TO DISINFECTANT 



One-tenth cubic centimeter of the culture is used, added to 5 cc. of the dis- 

 infectant dilution. The amount of culture is measured with a pipette grad- 

 uated in tenths of a cubic centimeter. 



INOCULATION LOOPS 



For making the transfer of the culture after exposure to the disinfectant a 

 platinum loop 4 millimeters in diameter of 23 United States standard gauge 

 wire is used. We have found it is of advantage to have at least four, and pref- 

 erably six, loops. In order to save time in flaming the following method was 

 devised : 



A block about 3 inches wide, 10 inches high, and 12 inches long, containing 

 four or six grooves, spaced 2 inches apart, is used. Into each of the grooves 



