HYGIENIC LABORATORY METHOD 149 
Inoculation Loops. For making the transfer of the culture after 
exposure to the disinfectant a platinum loop 4 mm. in diameter of 23 
United Statcs standard gauge wire is used. We.have found it is of 
advantage to have at least 4, and preferably 6, loops. In order to save 
time in flaming the following method was devised: 
A block about 3 ins. wide, 10 ins. high, and 12 ins. long, containing 
4 or 6 grooves, spaced 2 ins. apart, is used. Into each of the grooves 
the platinum loop is laid so that the end of the loops extend about 5 ins. 
beyond the side of the block. The first step in the operation is to ster- 
ilize 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 (fantail) 
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 fifteen seconds is ample. 
Incubation. The subcultures are incubated forty-eight hours at 
37° C., and the results then read off and tabulated. 
Dilutions. Capacity pipettes for the original dilutions are invariably 
used. For the phenol controls a standard dilution of pure phenol 
(‘“‘ Merck’s Silver Label’’) is made and standardized by the U. 8. 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 made 
by adding 5 c.c. of the disinfectant to 95 c.c. of sterile distilled water. 
A standardized 5 ¢.c. capacity pipette is used for this, and after filling 
the pipette all excess of the disinfectant on the outside of the pipette is 
wiped off with sterile gauze. The contents of the pipette are then 
delivered into a cylinder containing 95 c.c. of sterile distilled water and 
the pipette washed out as clean as possible by aspiration and blowing 
out the contents of the pipette into the cylinder. The contents of the 
cylinder are then thoroughly shaken and the dilutions up to 1 : 500 
made from it, using delivery pipettes for measuring. For those dis- 
infectants which do not readily form a 5 per cent solution we make a 
1 per cent stock solution, and from this make the dilutions greater than 
1: 100 in accordance with the second table of dilutions. If greater 
