176 STERILIZATION AND DISINFECTION 
tilled water and primary dilutions are to be made of such strength that 
the dose is easily measured with a 1-c.c. pipette graduated in hun- 
dredths. This is most easily accomplished by the use of the substance 
in greater concentration than that required to kill in the above volume 
dose. After the required dose of the diluted disinfectant has been 
estimated it is measured into a suitable dish and is then diluted further 
to the required volume by adding water in sufficient quantity. A series 
of mice are then to be injected with varying amounts of the substance 
until the least fatal dose is determined, the mice being kept under 
observation for a period of twenty-four hours unless death results in a 
shorter time. 
Mice of the same lot are similarly injected with pure phenol prop- 
erly diluted to make the measurement of the dose easy and then further 
diluted in a small dish to equal a volume dose of 0.03 to 0.04 ¢.c. per gram 
of body weight and the least fatal dose determined as above. The dose 
thus obtained is considered unity and the least fatal dose of the sub- 
stance in question is estimated in per cent of this, as is illustrated in the 
table following: 
Woes. PoP Bod Results. Time, 
Hrs Min 
Disinfectant A............ 21.13 0.0012 Survived 
20.64 0.0016 Survived 
18.32 0.0018 Lethal 10 30 
19.05 0.0020 Lethal 2 15 
Phenol. ..--.... cece eee ees 18.46 0.00035 Survived 
20.10 0.00040 Survived 
19.23 0.00045 Lethal 1 15 - 
18.90 0.00050 Lethal 0 25 
The least fatal dose of disinfectant A was estimated to be 0.0018; 
that of phenol 0.00045. The phenol toxicity coefficient of disinfectant A 
therefore is, according to the proportion 4.5 : 18:: x : 100, 25 per cent. 
The following are some toxicity coefficients secured by Hale in the 
application of his procedure to some commercial disinfectants. For 
the sake of comparison, the “ phenol coefficients ”’ as determined by 
McClintic have been included: 
