262 AIDS TO BACTERIOLOGY 



broth culture a fresh subculture is made in broth before 

 the former is used for the test. This subculturing into 

 fresh broth may and should be done every twenty-four 

 hours, whether a test is to be made or not. After a month 

 a fresh agar slope is made, and from the month-old agar 

 streak a fresh series of broth cultures started. 



All measures, pipettes, and tubes should be sterile, 

 and sterile distilled water must be used for making the 

 dilutions. 



The pipette used for delivering the three drops of 

 culture to the disinfectant dilutions should deliver O'l c.c. 

 per drop. The needle used should be composed of thin 

 aluminium rod, with a short piece of thin platinum wire 

 passed through and twisted round an eye in the end of 

 the rod. The free end of the wire is then made into 

 a loop about 4 millimetres in diameter. If the sides of 

 the loop be depressed so that in side-view it looks like 

 a cholera vibrio, the loop easily carries a big drop. Use 

 of a thin wire allows quick cooling. 



When subculturing, a good-sized drop (easily obtained 

 by bringing the loop away from the liquid with a jerk) 

 should always be taken up. 



The desired result in the phenol column is life in two 

 and a half minutes and in five minutes, and no life 

 thereafter. Rideal and Ainslie Walker (Medical Press, 

 September 15, 1915) suggest that a typhoid culture be 

 rejected if it calls for a phenol dilution higher than 

 1 in 110, or lower than 1 in 90. 



While the test is in progress, the temperature of the 

 medication tubes should not vary more than 2 C. When 

 tests are being performed on successive days, it is of 

 considerable help if the temperature of the room in which 

 the first test is done be known. Should the temperature 

 be higher the next time, a weaker phenol solution should 

 be used, or, if lower, a stronger one. 



Ainslie Walker (N.Y. Med. Journ., February 1, 1913) 

 points out that the use of bullock's heart broth instead 

 of Liebig broth has the effect of depressing a coefficient 

 by about 50 per cent. For further details of this test, 

 see ' The Bacteriological Examination of Disinfectants,' 

 by W. Partridge. 



A coefficient obtained on a freshly prepared emulsion is 

 termed a ' temporary coefficient,' but as frequently a 



