286 APPLIED BACTERIOLOGY 



apparently the same species, according to their previous 

 history, and for a single race at various ages. They are 

 quite different for developed organisms and for spores ; and 

 for each they may vary according as the organism is wet 

 or dried. The capacity to grow on media after contact 

 with inhibitory substances varies with the medium, and in 

 particular may differ as between culture media and living 

 animals. The number of organisms which can be disin- 

 fected by a given quantity of disinfectant is limited. The 

 action of the disinfectant is influenced by the temperature. 

 These sources of variation, if ignored, are naturally so 

 many sources of error in any generalisations from in- 

 dividual experiments on antiseptic or disinfectant action. 

 For any practical purpose, however, there are other com- 

 plications. An organism occurs in various environments, 

 which may sometimes be protective ; and substances 

 capable of affecting the organism may or may not affect 

 the bodies in its immediate neighbourhood, and produce 

 results on the joint inoculation of the organism with its 

 accidental envelope for the time being, which would not be 

 produced if the envelope were removed. The inhibitory 

 substance may adhere either to the organism itself or to 

 its envelope, and on inoculation prevent growth, when in 

 Nature the inhibitory substance might be ultimately re- 

 moved, and the organism resume its vegetative capacity 

 and its original virulence. 



Almost every one of these factors exercises an influence 

 on every disinfection experiment. But though we know 

 that variations in them may produce varying results in the 

 action of a disinfectant, we cannot at present say what 

 extent of variations in the conditions will produce a par- 

 ticular variation of the result. Thus, if a substance be 

 found, with all the conditions carefully noted, to exercise 

 a disinfectant action in a certain strength, no general 



