CHAPTER V. 



DESTRUCTION OF BACTERIA BY CHEMICALS 

 AND THEIR PRACTICAL USE. 



IT has been shown how bacteria can be killed by heat, 

 and now the chemical methods of destroying infective 

 material will be discussed, and how this may be done prac- 

 tically. Chemicals either in solution or as gas are supposed to 

 kill bacteria by one of several methods. The whole bacterial 

 body may be destroyed or the protoplasm may be entered by 

 a diffusion of the substance through the cell wall with conse- / 

 quent coagulation or solution. It is said also that the rapid 

 withdrawal of water absorbed by some salts may be fatal to 

 the microorganism. 



There is some confusion as to the terms used for chemical 

 bacteria killing, and for this reason it may be well to start 

 out with Park's classification. (1) Attenuation is when the 

 pathogenic or vital functions of the bacteria are temporarily 

 diminished. (2) Antiseptic action is when the bacteria are 

 not able to multiply but are not destroyed; they will repro- 

 duce when suitable conditions for life are restored. (3) 

 Incomplete sterilization or disinfection is when the vegetative 

 forms but not the spores are destroyed. (4) Sterilization or 

 disinfection is when both vegetative and spore forms are 

 destroyed; this implies also the destruction of any products 

 of bacteria capable of producing disease. 



Practical disinfection must provide not only for superficial 

 action but also for penetrative, and a disinfectant should be 

 selected which will act as deeply as possible. Formaldehyde 

 gas or its solution has a high penetrating power and is there- 

 fore commonly used for the disinfection of rooms, mattresses, 

 4 (49) 



