120 DISINFECTION— STERILIZATION— DISINFECTANTS 



result in the death of all organisms this necessitates a high 

 temperature, in itself destructive, and does not occur in 

 practice. Further, though many pathogenic bacteria are 

 killed by drying, many more, including the spore formers, 

 are not. Hence drying alone is not a practical method of 

 disinfecting. 



2. Heat. — ^The use of heat in some form is one of the 

 very best means for destroying bacteria. It may be made 

 use of by combustion, or burning, as direct exposure to the 

 open flame, as dry heat (hot air), or as moist heat (boiling 



Fig. 76. — A small laboratory hot-air sterilizer. 



water or steam). Very frequently in veterinary practice, 

 especially in the country, occasionally under other condi- 

 tions, the infected material is best burned. This method is 

 thoroughly effective and frequently the cheapest in the end. 

 Wherever there are no valid objections it should be used. 

 Exposure to the open flame is largely a laboratory procedure 

 to sterilize small metallic instruments and even small pieces 

 of glassware. It is an excellent procedure in postmortem 

 examinations to burn off the surface of the body or of an 

 organ when it is desired to obtain bacteria from the interior 

 free from contamination with surface organisms. 



