234 BACTERIOLOGICAL METHODS 



Proportion of Culture to Disinfectant. — One-tenth cc. of the 

 culture is used, added to 5 cc. of the disinfectant dilution. The 

 amount of culture is measured with a pipette graduated in tenths 

 of a cubic centimeter. 



Inoculation Loops. — For making the transfer of the culture 

 after exposure to the disinfectant a platinum loop 4 mm. in diam- 

 eter of 23 U. S. standard gauge wire is used. We have found it 

 of advantage to have at least four, and preferably six, loops. In 

 order to save time in flaming the following method was devised: 

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

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

 grooves the platinum loop is laid so that the ends of the loops 

 extend about 5 in. beyond the side of the block. The first step 

 in the operation is to sterilize each loop by flaming with a fantail 

 Bunsen burner before beginning the experiment. 



When ready to begin the operation the loop farthest from the 

 operator is taken in the right hand and the inoculation made. 

 It is then replaced in the groove with the right hand and the 

 Bunsen burner (fan tail) placed under it with the left hand. The 

 next loop is then used, replaced in its groove, and the Bunsen 

 burner placed under it with the left hand, the first loop having 

 been heated to redness while the second loop was in use. This 

 procedure is then continued until all the inoculations have been 

 made. The time required in making the inoculations and in 

 replacing the loop is short, it being found that 15 sec. is ample. 

 Incubations. — The subcultures are incubated 45 hr. at 37° 

 C, and the results then read off and tabulated. 



Dilution. — Capacity pipettes for the original dilutions are 

 invariably used. For the phenol controls a standard dilution 

 of pure phenol (Merck) is made and standardized by the U. S. 

 P. Method (Koppeschaar) to contain exactly 5 per cent, of pure 

 phenol by weight. From this stock solution the higher dilutions 

 are made fresh each day for that day's test. 



For the dilutions of the disinfectant a 5 per cent, solution is 



