CHAPTER XXVIII. 



Methods of testing disinfectants and antiseptics— Experiments illustrating 

 the precautions to be taken— Experiments in skin disinfection. 



There are several ways of determining the germicidal 

 value of chemical substances, the most common being 

 to expose organisms dried upon bits of silk thread to 

 the disinfectant for diiferent lengths of time, and then, 

 after removing, and carefully washing the threads in 

 water, to place them into nutrient media at a favorable 

 temperature, and notice if any gro^\•th appears. If no 

 growth results the disinfection is presumably success- 

 ful. Another method is to mix fluid cultures of bacteria 

 with the disinfectant in varying proportions, and, after 

 different intervals of time, to determine if disinfection 

 is in progress by transferring a portion of the mixture 

 to nutrient media, just as in the other method of work. 



By the former process the bits of thread, usually 

 about 1 to 2 cm. long, are placed in a dry test-tube pro- 

 vided with a cotton plug and carefully sterilized, either 

 by the dry method or in the steam sterilizer, before 

 using. They are then immersed in a pure bouillon 

 cnlture or in a salt solution suspension of the organism 

 upon which the disinfectant is to be tested. I say pure 

 culture because it is always desirable in testing a new 

 germicide to determine its value as such on several 

 different resistant species of bacteria, both in the vege- 

 tating and in the spore stage. After the threads have 

 remained in the culture or suspension for, from five to 



