20 



BACTERIOLOGY FOR NURSES 



Sterilization. Properly, sterilization means the 

 complete destruction of bacteria, by whatever means; 

 but by custom in the laboratory sterilization is used 

 when heat is the agent employed, and disinfection is 

 used to designate sterilization by chemicals. 



Sterilization by heat may be accomplished by dry 

 heat, as by baking or passing an object through a 

 flame, or by moist heat, such 

 as boiling, or by steam, with or 

 without pressure. Sterilization 

 by heat is commonly employed 

 for the sterilization of utensils, 

 instruments, and culture media, 

 as the action of chemicals 

 would be unfavorable to the 

 cultivation of bacteria; but 

 chemicals are used for disin- 

 fecting the hands, old cultures, 

 and all useless infective materials. 



It is estimated that bacteria and spores exposed to 

 a temperature of 170 C. (338 F.) for one hour will 

 be completely destroyed. 



There are a number of hot-air sterilizers in com- 

 mon use which give a uniform heat in all parts of 

 the oven. 

 Sterilization by steam under pressure is accom- 



FIG. 5. Laboratory hot- 

 air sterilizer. 



