BACTERICIDAL PROPERTIES 15 



1. Type op OrGx\nism. — In the early days of antisep- 

 sis, disinfectants were tested baeteriologieaily with the 

 idea of discovering some chemical agent that Avould 

 destroy all known bacteria when nsed in a weak solution. 

 No such universal antiseptic has been found. On the 

 contrary, it has been found that different antiseptics 

 have a selective action upon certain types of organisms. 

 For example, bichlorid of mercury is a most powerful 

 disinfectant for anthrax, but has only a weak action 

 on tubercle bacilli and is much less effective than some 

 other drugs (creolin, lysol, alcohol) for superficial dis- 

 infection of the skin, while carbolic acid is relatively 

 ineffective against tetanus bacilli, anthrax spores, and 

 tubercle bacilli. It therefore follows that in disinfec- 

 tion the different organisms and bacteria must be con- 

 sidered individually. In general, it can be said that 

 spore-bearing bacteria require stronger disinfectants 

 than non-spore bearers. Here again individual differ- 

 ences in resistance of species of spores and vegetative 

 forms manifest themselves. It is, therefore, difficult to 

 make a comparative table of individual drugs. In gen- 

 eral, the strongest disinfectants w^hich also destroy spores 

 are mercuric chlorid, silver nitrate, iodin, creolin, lysol, 

 liquor cresolis compound and other cresol preparations, 

 and formalin. The weaker disinfectants which kill only 

 spore-free organisms are coal tar, carbolic acid, salicylic 

 acid, dyes, boric acid, and calcium lyes (whitewash) and 

 acids. 



Individual Resistance of Organisms. — The individual 

 resistance of different organisms varies. Some infectious 

 agents are very readily destroyed w^hile others are very 

 resistant. For practical purposes disease-producing 

 micro-organisms may be divided into two groups on the 

 basis of their power to resist disinfection. 



