292 APPLIED BACTERIOLOGY 



either in broth or in sterile distilled water, and to inoculate 

 these threads, usually after drying, into solutions of the 

 disinfectant. This method is unsatisfactory, in that • it 

 affords no means of maintaining a standard relation between 

 the number of organisms and the quantity of disinfectant, 

 because the penetration of a disinfectant into the depths of 

 the thread has been found to be notably irregular, and 

 because traces of the disinfectant are extremely liable to 

 adhere to the thread. Endeavours have been made to avoid 

 the difficulty by washing the threads in sterile water until 

 it is to be presumed that the disinfectant has disappeared. 

 The presumption, however, is very apt to fail. With some 

 disinfectants it is possible to form by the addition of a 

 substance possessing no disinfectant capacity an iaert in- 

 soluble compound ; and attempts have been made to avoid 

 the transfer of disinfectant with the organisms on the thread 

 by applying such treatment. For example, it has been usual 

 to wash the threads exposed to perchloride of mercury with 

 ammonium sulphide. Irregular penetration, however, of 

 the disinfectant makes it quite possible that some portions 

 may not be reached by this process. The objections to this 

 method are to a considerable degree removed when threads 

 of slag-wool are used instead of silk. 



It is found that the action of a disinfectant is enhanced 

 in most cases by its application at a higher temperature 

 than 15° C, even when that temperature is below such as 

 would not itself injure the organism. It is also found in 

 many cases that two separate disinfectants exercise a more 

 powerful effect, and work in much weaker solutions than 

 either of them separately. The action, however, of a 

 disinfectant may be impeded by other substances in which 

 it is conveyed. For instance, the presence of soap, which 

 in itself possesses some disinfectant capacity, is liable to 

 impede the action of mercuric perchloride ; and most 



