DETERMINATION OF PENETRATING POWER 163 
It will be seen that the disinfectant Chl has a higher coefficient than 
any of the others in the table, but its higher cost per gallon results in 
its being placed second in cost per 100 units of efficiency. 
When bids are solicited for supplying disinfectants they should be 
required to be made so as to show the cost per 100 units of efficiency 
of the disinfectant as compared with the cost of 100 units of efficiency 
of pure phenol. In that way only can a contract for supplying disin- 
fectants be awarded in the combined interests of economy and effi- 
ciency. , 
It may be proper to state here that in the specifications for bids for 
supplies for the fiscal year beginning July 1, 1912, prepared by the 
General Supply Committee, is the following specification for bids on 
disinfectants: 
Item 4136 (d), noncorrosive, cresol, phenol, or analogous compound; must 
be uniform material at 43° F. and ‘dilute with water and form a practically 
perfect emulsion or solution and have a phenol coefficient accordmg to present 
method of Hygienic Laboratory of not less than 2; 1 gal. sample required. 
Notre.—The phenol coefficient of disinfectants on which bids are made must be 
stated. 
The Gencral Supply Committee prepares specifications on which 
bids are solicited for supplies for all the departments in Washington. 
McClintic (1912) determined the phenol coefficient of some common 
disinfectants. The results are indicated in Table XVITI. 
Kendall and Edward’s Method for Determining Penetrating Power. 
The authors have attempted to broaden the standardization of dis- 
infectants by determining the relative penetrating power of these agents. 
The important features of the Rideal-Walker method are retained. 
(1) Prepare a twenty-four-hour culture of B.Colz in plain broth 
of standard composition and reaction; (2) add 10 c.c. of this standard 
culture to 1 liter of agar (1.5 per cent agar) and mix thoroughly; (8) 
pour the infected agar into sterile tubes of convenient length (1 meter) 
and of exactly 1.5 em. diameter and allow to harden, after closing the 
ends with sterile rubber stoppers; (4) allow to harden at 20° C.; (5) 
prepare dilutions of the desired disinfectants and a standard 5 per cent 
carbolie acid solution—the latter is the standard to which the other 
disinfectants are referred; (6) place the disinfectants so prepared in 
sterile beakers, allowing 50 c.c. for each agar cylinder; (7) remove 
stoppers from the infected agar tubes, and permit the contents to run 
out slowly as a long cylinder; with a sterile knife cut off portions by 
transverse cuts of 2 cm. length, and allow these smaller cylinders to 
