DISINFECTANTS AND DISINFECTION 



335 



dredths. This is most easily accomplished by the use of the substance in 

 greater concentration than is required to kill in the above volume 

 doses. 



Administration of the Test Solutions. 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 sterile dis- 

 tilled water in sufficient quantity. A series of mice are then injected 

 subcutaneously with varying amounts of the substance until the least 

 fatal dose (L.F.D.) is determined, the mice being kept under observation. 



Time Limit of the Observation. After the animals have been inoculated 

 they are kept under observation for a period of 24 hours unless death 

 results in a shorter period of time. 



Phenol Comparative Test. Mice of the same lot are similarly injected 

 with pure phenol properly diluted to make the measurements of the dose 

 easy and then further diluted in a small dish to equal a volume dose of 

 0.03 to 0.04 c.c. per gram of body weight and the fatal dose determined as 

 above. This least fatal dose (L.F.D.) of phenol is unity and the least fatal 

 dose of the substance in question is estimated in per cent, of this. 



Determining the Comparative Toxicity. The phenol toxicity of the dis- 

 infectant tested is to the toxicity of phenol as x is to 100. The example 

 given below would be represented in the following proportion 4.5: 

 18 ::x : 100 = 25 per cent., that is disinfectant "A" is one-fourth as 

 toxic as is pure phenol. 



Valuable information regarding the comparative toxicity of many of 

 the substances used as disinfectants may be obtained from a study of the 

 comparative medicinal doses. For example, the doses of phenol, betol, 

 resorcinol and corrosive sublimate are i grain, 3 grains, 4 grains and 

 Jio grain respectively. These doses are pract'cally in proportion to the 

 toxicity of the substances named and stating the dosage in the terms of 



