The Effect of Chemicals on Microorganisms 199 



tions) are employed in preference to aqueous (water) solutions 

 when treating cuts and wounds with disinfectants. Alcohol has a 

 much lower surface tension than water, and it can thus be con- 

 sidered to be wetter than water. So-called wetting agents, includ- 

 ing Lauryl Sulfate, Tween 80, and Tergitol 7, can be incorporated 

 into liquids to improve their wetting power and penetrating ability. 



8. Moderate Cost. If a compound is priced excessively high, 

 it will be restricted in its usefulness. While price is a relative 

 thing, there are limits if the product is to be put on the market for 

 common use. 



Other considerations may be added to this list characterizing 

 an ideal disinfectant, but they would probably not be nearly as 

 important as the factors already discussed. Some compounds ap- 

 proach being ideal as disinfectants, but none of them fulfills all 

 of the desired characteristics. 



FACTORS INFLUENCING DISINFECTION 



Disinfection is in part a chemical reaction, and factors in- 

 fluencing chemical reactions will, in general, affect the disinfection 

 process. It is agreed that temperature, time, moisture, concen- 

 tration of reacting substances, presence of extraneous matter, and 

 surface tension have a direct bearing on the outcome of this chemi- 

 cal change. Undoubtedly there are other factors which are in- 

 volved, but a brief statement about each of the above six con- 

 siderations seems warranted. 



1. Temperature. The speed of a chemical reaction will in- 

 crease with the temperature up to a certain point. Many chemical 

 reactions will go to completion in a matter of a few minutes under 

 the influence of heat, but these same reactions at room temperature 

 or lower, might require days, weeks, months, or even years, if they 

 took place at all. Heat may be considered to act like a catalyst 

 when it accelerates the speed of a reaction. 



2. Time. The most rapid chemical reactions known to man 

 require time to occur. Disinfection is not instantaneous, although 

 this is a common misconception. Many persons firmly believe that 



