APPENDIX 473 



cresol mixture above noted that action of the disinfectant should continue at least 

 one hour before emptying the vessel. 



(3) Nature of medium in which disinfectant acts. Bacteria are much more re- 

 sistant to germicide agents when contained in solution rich in organic matter than 

 when suspended in pure water. Thus Liq. Cresol. Comp. has a phenol coefficient 

 of 3 without organic matter and only 1.87 with organic matter. 



(4) Temperatures. Disinfecting solutions show greater power as the temperature 

 rises, and act less efficiently in the cold. A body temperature (3QC.) is a good 

 one. 



By Coefficient of Inhibition we mean time and concentration necessary to prevent 

 development of bacteria. 



By Inferior Lethal Coefficient we mean time and concentration necessary to kill 

 nonspore-bearing bacteria. 



By Superior Lethal Coefficient we mean time and concentration necessary to 

 kill spore-bearing bacteria. 



U. S. Hygienic Laboratory Phenol Coefficient. In determining the strength of a 

 disinfectant it is compared with that of phenol (commercial carbolic acids vary in 

 their phenol content). If more powerful than phenol the coefficient will be greater 

 than i. In the U. S., disinfectants are rated according to the "Hygienic Laboratory 

 Phenol Coefficient." 



The determinations when organic matter was not present, were conducted as 

 follows : 



"The experiments were done at a temperature of 2oC. maintained by means of a 

 water-bath. The quantity of each dilution of disinfectant and phenol used in each 

 experiment was 5 c.c. The culture used was B. typhosus, twenty-four-hour 

 extract broth, filtered. The seeding tubes containing the disinfectant dilutions and 

 the filtered broth culture of B. typhosus were placed in the water-bath and allowed 

 to reach the temperature of 2oC. before starting the experiment. 



" The seeding tubes were inoculated successively every fifteen seconds with o.i c.c. 

 of the typhoid culture. Each tube was gently shaken after it was inoculated. At 

 the end of each two and one-half minute period, for fifteen minutes, plants were 

 made from the seeding tubes into tubes of extract broth. The medium used was 

 standard extract broth having a reaction of +1.5. The quantity of broth in each 

 tube was approximately 10 c.c. 



"The tubes were incubated at 37C. for forty-eight hours, at the end of which 

 the results were recorded. 



" To determine the coefficient, the figure representing the degree of dilution of the 

 weakest strength of the disinfectant that kills within two and one-half minutes is 

 divided by the figure representing the degree of dilution of the weakest strength of 

 the phenol control that kills within the same time. The same is done for the 

 weakest strength that kills within .fifteen minutes. The mean of the two is the 

 coefficient. 



" When the determinations were made as to efficiency in the presence of organic 

 matter a stock solution of 10% peptone and 5% gelatin in water was made up and 

 of this i c.c. was put in a tube and then inoculated with o.i c.c. of typhoid culture. 

 Then 4 c.c. of the varying phenol and disinfectant dilutions were added and the 

 tests conducted as above." 



