HYGIENIC LABORATORY METHOD 161 
of organic matter, plus 0.1 ¢.c. of typhoid culture, and that the quan- 
tity of organic matter represented is 3 per cent. 
In computing the strengths of the disinfectant and the percentage 
of organic matter present in the seeding tubes when the test is made, 
we have disregarded the slight change resulting from the addition of the 
0.1 c.c. of typhoid culture to each tube. By so doing the experiment 
is very much simplified, as it would be very difficult to prepare the 
dilutions of the disinfectant on the basis of allowing for so slight a 
change as is caused by the addition of 0.1 c.c. of liquid. 
Many of the details of conducting the experiment and the method 
of determining the coefficient will be seen in Table No. 16: 
TaBLe XVI 
Name, “A.” 
Temperature of medication, 20° C. 
Culture used, B. typhosus, twenty-four-hour, extract broth,, filtered. 
Proportion of culture, organic matter and disinfectant, 0.1 ¢.c. +1 ¢¢.+4 «ae 
Percentage of organic matter, 2 per cent peptone and I per cent gelatin. 
Total percentage of organic matter, 3 per cent. 
Time Culture Exposed to Action 
Sample. Dilution of Disinfectant for Minutes Phen ol coef 
23 | 5 | 7} | 10 | 124 | 15 
Phenol..............0000- 1:80 —f—]— 180 . 375 
- /1:90 |} +) +/—-—-;-—-/)}—]-—)] 86 90 _ 
1:10) 4+ )/+/}/+/)+/)+)+] 737 
1:110; +/+) +;),+),+/4+ 
2.25+4.17 | 
Disinfectant ‘‘A’”......... 1:180}; ~ |} —i — a, 
1:200/;+;-—{-—- — ie 
1:225); +l —)—} me} 
1:250; +;);—-—-]— —~ | — 
1:300; +i) +i -i—-j—-jf-— 
1:325;); +) +) —)-}—-] - 
1:350; +) +/4+),—-{;—-)] - 
1:375;) +; +/4+/)4+/-j- 
1:400; +i +) titi ti t+ 
1:45) +/+} +); +/)+/4 
en anos ptm eee deer aimboIn ema ert He A MANE maN thE ON ON ti ERRNO aman 
To Determine the Cost of a Disinfectant per Unit of Disinfecting ~ 
Efficiency as Compared with Pure Phenol. It is manifestly cheaper to 
purchase a disinfectant for 60 cents a gallon than it is to purchase one 
for 30 cents a gallon, provided the former has four times the efficiency of 
the latter. The true cost of a disinfectant can only be determined by 
