CHAPTER VI 

 RELATION OF BACTERIA TO DESTRUCTIVE INFLUENCES 



DISINFECTANTS AND ANTISEPTICS 



IN a previous chapter it was pointed out that bacteria 

 required a certain degree of heat in order to thrive. 

 For most pathogenic bacteria this is about 100 F. 

 Higher temperatures, on the other hand, exert an in- 

 jurious action on bacteria, so that even a short ex- 

 posure to the temperature of boiling water quickly 

 kills most pathogenic bacteria. Destruction of bacteria 

 can also be effected by prolonged exposure to tempera- 

 tures considerably less than the boiling-point of water. 

 This is spoken of as "pasteurization," after Pasteur, 

 who first applied this method of killing bacteria. The 

 effect of low temperatures on bacteria varies consider- 

 ably with different species. Bacteria accustomed to 

 grow at body temperature usually cease to grow or 

 grow very slowly at ordinary room temperatures. 

 There is practically no growth at all at 40 F. At 

 freezing temperature many bacteria die off, but even 

 the low temperature of liquid air does not certainly 

 kill all forms. 



Bacteria also vary in their resistance to drying, the 

 vegetative forms usually drying quickly, while certain 

 spore forms appear to resist drying indefinitely. As 

 has already been pointed out, direct sunlight exerts a 



