198 Microbes and You 



fectants are to be applied. The chemical should not spontaneously 

 break down upon standing, or the decomposition products may 

 have little or no lethal effect, and the user may be left with a false 

 sense of security. 



3. Homogeneity. Every drop of the disinfectant should be 

 just as effective in its killing capacity as every other drop in the 

 container. Whenever the label calls for shaking the compound 

 well before using, the human element is introduced and interpreta- 

 tions of "shake well before using" vary widely from person to 

 person. 



4. Ready Solubility in the Strength Required for Disinfection. 

 If a compound is to be employed as a disinfectant, it must, in 

 many cases, ionize (dissociate into ions). To do this the chemical 

 must be soluble in the concentration that is toxic for microorgan- 

 isms. 



5. Non-Poisonous to Higher Animals and Man. The narrow 

 margin existing between the concentration of medication required 

 to kill microorganisms and the strength of the chemical that de- 

 stroys healthy tissue cells of the host limits the usefulness of some 

 compounds that have a high germicidal power. Not only must the 

 bacteria be killed when the disinfectant is applied, but healthy 

 tissues should be kept intact, if possible, to speed subsequent heal- 

 ing of the wound. If the chemical is readily absorbed into the 

 animal system and has lethal effects on internal organs, the appli- 

 cation of the disinfectant must be confined to use on inanimate 

 objects. 



6. Noncorrosive. This is mainly a storage problem, but if the 

 disinfectant is to be used on metals, such as in operating rooms, 

 etc., any corrosive action may so damage the equipment that it 

 becomes impractical to use an otherwise effective agent. 



7. Penetrative Power. Liquids exhibiting low surface tension 

 have greater penetrating power than high surface tension sub- 

 stances. In order to reach bacteria that are deeply entrenched in 

 a wound, penetrating power of the agent is an important factor. 

 It is for this reason, among others, that tinctures (alcoholic solu- 



