ANTISEPTIC AND GERMICIDAL POWER 155 



Organic matter may influence the potency of a disinfectant 

 in a number of ways. In some cases the disinfectant is used up 

 by acting as an oxidiser to the organic matter, in others the two 

 form an inert compound, while in a further group of cases the 

 action of the organic matter would appear to be largely or at 

 least in part due to its effect upon the emulsification of the 

 disinfectant, accelerating or retarding it. 



Martin and Chick 1 showed that the presence of particulate 

 organic matter, such as animal charcoal or faeces, affected the 

 germicidal value of emulsified tar acid disinfectants to a much 

 greater extent than it did phenol solution. By the suitable 

 addition of such particulate organic matter the whole of the 

 emulsified tar acid could be removed. When a 3 per cent, 

 suspension of dried finely-divided faeces is used the efficiency of 

 phenol is only reduced by about 10 per cent., while that of the 

 emulsified tar acids is reduced from one-third to one-eleventh of 

 the primary value. The soluble commercial cresols occupy an 

 intermediate position, the reduction depending upon the solu- 

 bility. The reduction in the case of the emulsified tar acids 

 they found to be higher the finer the emulsion. Some dis- 

 infectants are more efficient against one species of bacterium, 

 others against another. In the case of spores metallic salts are 

 most efficient. The removal of an emulsion of higher phenols 

 by bacteria is in the first instance a process of adsorption ; dis- 

 infectants which form fine emulsions possess superior efficiency, 

 because, owing to this adsorption, the bacteria rapidly become 

 surrounded by the disinfectant in much greater concentration 

 than exists throughout the liquid. 



The Rideal- Walker method does not take into account the 

 influence of the presence of organic matter, and various attempts 

 have been made to obviate this difficulty. For this purpose 

 the addition of gelatine, serum, urine, milk, faeces, etc., has been 

 suggested by different workers, so that the germicidal power of 

 the disinfectant may be tested in the presence of organic matter. 

 None of these additions are altogether satisfactory, and it cannot 

 be said that a suitable method has yet been evolved. The effect 



1 f our nal of Hygiene, 1908, vol. vin, p. 654^ 



