GERMICIDAL POWER OF CHEMICAL DISINFECTANTS 189 



ORGANIC MATTER 



Under practical conditions disinfectants are commonly used in the presence 

 of more or less organic matter. It is therefore very important to know to what 

 extent the germicidal efficiency of a disinfectant is affected by the presence of 

 organic matters. 



The character and quality of organic matter present as well as its effect upon 

 the germicidal efficiency of different disinfectants are such widely varying 

 factors that the standardization of disinfectants in the presence of organic 

 matter is a rather difficult problem. We have done a great deal of experimental 

 work with disinfectants in which various kinds of organic matter were tried, 

 and it has been difficult to find a form of organic matter that is entirely satis- 

 factory for standardization purposes. Urine, blood serum, dead (killed by 

 heat) broth cultures of the typhoid bacillus, peptone, gelatin, egg albumen, 

 starch, etc., were all given a trial and we have finally decided to use a mixture 

 of an aqueous solution of peptone and gelatin. 



It is manifestly necessary that any form of organic matter, used for stand- 

 ardization of disinfectants, be of known, definite composition. Unless this is 

 the case only widely varying results can be expected. A mixture of urine and 

 feces would probably simulate the natural conditions under which disinfectants 

 are ordinarily used more closely than any of the other forms of organic matter, 

 but the organic content of different specimens of urine and feces is so variable 

 as to practically exclude their use in standardization work. Blood serum is 

 constant in composition, but it is often difficult to obtain, particularly in a 

 sterile condition, and, of course, organic matter must be sterile when it is used. 



The results obtained with starch and with egg albumen used as organic 

 matter were, on the whole, unsatisfactory. 



Dead broth cultures of the typhoid bacillus and the peptone-gelatin mixture 

 gave rather similar results, but on account of the ease with which the latter can 

 be procured and prepared we have chosen it for use in our work. Peptone and 

 gelatin are fairly constant in composition, and a mixture of the two can be 

 sterilized without altering the composition of either the peptone or the gelatin. 



HYGIENIC LABORATORY PHENOL COEFFICIENT 

 A. Without Organic Matter 



Having discussed the necessity for a satisfactory method of standardizing 

 disinfectants and the factors involved in the examination of disinfectants, we 

 present below the method we have devised. 



When this method is used for the standardization of disinfectants we recom- 

 mend that it be referred to as the "Hygienic Laboratory phenol coefficient." 



We prefer to use the word "phenol" instead of "carbolic acid" when speak- 

 ing of the coefficient, especially since certain dealers advertise for sale carbolic 

 acids which vary greatly in the proportion of phenol present. 



