150 DISINFECTION AND STERILIZATION 



tated by albuminous substances and if employed at all must 

 be used in several times the ordinary strength. Solids 

 require relatively more of a given solution than liquids. 



7. State of the disinfectant, whether solid, liquid or gas, 

 and whether it is ionized or not. Solutions penetrate best 

 and are therefore more quickly active and more efficient. 



8. The solvent. Water is the best solvent to use. Strong 

 alcohol (90 per cent +) diminishes the effect of carbolic 

 acid, formaldehyde and bichloride of mercury. Oil has a 

 similar effect. The action is probably to prevent the pene- 

 tration of the disinfectant. 



9. Strength of solution. The stronger the solution the 

 more rapid and more certain the action, for the same reason 

 as mentioned under 5. In fact, every disinfectant has a 

 strength below the lethal at which it stimulates bacterial 

 growth. 



10. Addition of salts. Common salt favors the action of 

 bichloride of mercury and also of carbolic acid. Other salts 

 may hinder by precipitating the disinfectant. 



11. Temperature. Chemical disinfectants, as a rule, fol- 

 low the general law that chemical action increases with 

 the temperature up to the point where the heat of itself is 

 sufficient to kill. 



12. Time of action. It is scarcely necessary to point out 

 that a certain length of time is necessary for any disinfec- 

 tant to act. One may touch a red-hot stove and not be 

 burned. All the above-mentioned conditions are influenced 

 by the time of action. 



STANDARDIZATION OF DISINFECTANTS— 

 "PHENOL COEFFICIENT." 



Many attempts have been made to devise standard 

 methods for testing the relative strengths of disinfectants. 

 The one most widely used in the United States is the so-called 

 "Hygienic Laboratory" method of determining the ''phenol 

 coefficient" of the given substance and is a modification 

 of the method originally proposed by Rideal and Walker 

 in England. In this method as proposed by Anderson 



