212 Microbes and You 



mate use of the chemical is directed toward kilHng pathogens in 

 excreta and wastes, the test organism is customarily the typhoid 

 organism— Salmonella typhosa. On the other hand, if the chemical 

 is designed for use on the skin and in wounds, the more appro- 

 priate skin organism, Micrococcus pyogenes var. aureus, is em- 

 ployed in the test. 



The bactericidal strength of the chemical is expressed as a 

 number. With phenol, the standard, being assigned the number 

 1.0, a chemical having a coefficient higher than 1.0 can be said to 

 have greater killing power than phenol under the standard con- 

 ditions of this test, while coefficients less than 1.0 indicate that the 

 test material is less effective than phenol under these specific con- 

 ditions. The phenol coefficient is derived by determining how 

 high substance "X" can be diluted and still exhibit a lethal effect 

 equal to phenol. For example, if a 1:500 dilution of "X" produces 

 killing comparable to that of a 1:100 dilution of phenol, the 

 coefficient would be 500 divided by 100, or 5.0. 



There are many exact details which must be borne in mind 

 when conducting a phenol coefficient test. Interested students 

 are referred to advanced texts in the field for additional infor- 

 mation. 



SOAPS AND DETERGENTS 



The importance of soap and water in sanitary practices for 

 preventing the dissemination of pathogenic microorganisms can- 

 not be over-emphasized. While soaps as a group possess little or 

 no disinfecting power, they are capable of mechanically loosening 

 and removing "dirt" and organisms trapped in this material. The 

 term "sanitizing" has come into popular use in recent years, and 

 the expression has considerable merit. Too often people have 

 the false notion that dishes are sterilized when they are washed in 

 hot soapy water. The temperature of the water must be well above 

 that tolerated by human hands before disinfection can occur, to 

 say nothing of sterilization. When dishes and equipment are 

 sanitized, the visible organic matter is removed and pathogenic 

 bacteria find conditions unfavorable for their multiplication or even 

 their residence. It is unnecessary to sterilize eating utensils to 



